CN106486574B

CN106486574B - Light-emitting element with photoluminescent layer

Info

Publication number: CN106486574B
Application number: CN201610701607.1A
Authority: CN
Inventors: 稻田安寿; 平泽拓
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2015-08-27
Filing date: 2016-08-22
Publication date: 2020-04-28
Anticipated expiration: 2036-08-22
Also published as: JP2017045026A; CN106486574A

Abstract

Provided is a light-emitting element having a new configuration using a photoluminescent material. The light-emitting element includes: a light-transmitting layer having a first surface; a photoluminescent layer located on the first surface, having a second surface on the side of the light-transmitting layer and a third surface on the opposite side, receiving excitation light and emitting from the third surface Including the light of the first light. The photoluminescent layer has a first surface structure including a plurality of convex portions on the third surface. The light-transmitting layer has a second surface structure including a plurality of convex portions on the first surface. The first surface structure and the second surface structure restrict the directivity angle of the first light emitted from the third surface. In a cross section perpendicular to the photoluminescent layer and parallel to the arrangement direction of the plurality of convex portions in the first surface structure, the width of the base portion of the first convex portion among the plurality of convex portions in the first surface structure is wider than that of the top portion. Great width.

Description

Light-emitting element having photoluminescent layer

Technical Field

The present invention relates to a light-emitting element, and more particularly to a light-emitting element having a photoluminescent (photoluminescent) layer.

Background

In optical devices such as lighting equipment, displays, and projectors, it is required to emit light in a desired direction in many applications. Photoluminescent materials used in fluorescent lamps, white LEDs, and the like emit light isotropically. Thus, such a material is used together with an optical member such as a reflector or a lens in order to emit light only in a specific direction. For example, patent document 1 discloses an illumination system in which directivity is ensured by using a light distribution plate and an auxiliary reflection plate.

Patent document 1: japanese patent laid-open publication No. 2010-231941

Disclosure of Invention

Problems to be solved by the invention

In an optical apparatus, if an optical component such as a reflector or a lens is disposed, the size of the optical apparatus itself needs to be increased in order to secure a space for the optical component. It is desirable to eliminate these optical components, or at least to miniaturize them.

The present invention provides a light-emitting element having a novel structure using a photoluminescent material.

A light-emitting element according to an embodiment of the present invention includes: a light transmitting layer having a 1 st surface; a photoluminescent layer on the 1 st surface, having a 2 nd surface on the light-transmitting layer side and a 3 rd surface opposite to the 2 nd surface, and emitting light including a wavelength λ in air from the 3 rd surface upon receiving excitation light_aThe 1 st light of (1). The photoluminescent layer has a 1 st surface structure including a plurality of projections on the 3 rd surface. The light-transmitting layer has a 2 nd surface structure including a plurality of convex portions corresponding to the plurality of convex portions on the 1 st surface. The 1 st surface structure and the 2 nd surface structure limit a pointing angle of the 1 st light emitted from the 3 rd surface. The plurality of projections in the 1 st surface structure include a 1 st projection. In a cross section perpendicular to the photoluminescent layer and parallel to an arrangement direction of the plurality of convex portions in the 1 st surface structure, a width of a base portion of the 1 st convex portion is larger than a width of a top portion.

The above-described inclusion or detailed aspects may also be achieved by an element, an apparatus, a system, a method, or any combination thereof.

Effects of the invention

According to the embodiment of the present invention, a light-emitting element having a new configuration using a photoluminescent material can be provided.

Drawings

Fig. 1A is a perspective view showing a structure of a light-emitting element according to an embodiment.

Fig. 1B is a partial sectional view of the light-emitting element shown in fig. 1A.

Fig. 1C is a perspective view showing a structure of a light-emitting element according to another embodiment.

Fig. 1D is a partial sectional view of the light-emitting element shown in fig. 1C.

Fig. 2 is a graph showing the results of calculating the degree of enhancement of light emitted in the front direction by changing the emission wavelength and the period of the periodic structure.

Fig. 3 is a graph illustrating conditions under which m is 1 and m is 3 in formula (10).

Fig. 4 is a graph showing the results of calculating the degree of enhancement of light output in the front direction by changing the light emission wavelength and the thickness t of the photoluminescent layer.

Fig. 5A is a graph showing the result of calculating the electric field distribution of the mode guided in the x direction when the thickness t is 238 nm.

Fig. 5B is a graph showing the result of calculating the electric field distribution of the mode guided in the x direction when the thickness t is 539 nm.

Fig. 5C is a graph showing the result of calculating the electric field distribution of the mode guided in the x direction when the thickness t is 300 nm.

Fig. 6 is a graph showing the results of calculating the degree of enhancement of light in the case where the polarized light of light is the TE mode having an electric field component perpendicular to the y direction under the same conditions as in the calculation of fig. 2.

Fig. 7A is a plan view showing an example of a 2-dimensional periodic structure.

Fig. 7B is a diagram showing the result of performing the same calculation as in fig. 2 with respect to the 2-dimensional periodic structure.

Fig. 8 is a graph showing the results of calculating the degree of enhancement of light output in the front direction by changing the emission wavelength and the refractive index of the periodic structure.

Fig. 9 is a graph showing the results when the thickness of the photoluminescent layer was set to 1000nm under the same conditions as in fig. 8.

Fig. 10 is a graph showing the results of calculating the degree of enhancement of light output in the front direction by changing the emission wavelength and the height of the periodic structure.

FIG. 11 shows a periodic structure having a refractive index n under the same conditions as in FIG. 10_pA graph of the calculation results in the case of 2.0.

Fig. 12 is a diagram showing the results of performing the same calculation as that shown in fig. 9 assuming that the polarized light of the light is a TE mode having an electric field component perpendicular to the y direction.

FIG. 13 shows the refractive index n of the photoluminescent layer under the same calculation conditions as shown in FIG. 9_wavFig. 1.5 shows the result.

Fig. 14 is a graph showing the calculation results in the case where the photoluminescent layer and the periodic structure are provided on the transparent substrate having the refractive index of 1.5 under the same conditions as those of the calculation shown in fig. 2.

Fig. 15 is a graph illustrating the condition of equation (15).

Fig. 16 is a diagram showing a configuration example of a light-emitting device 200 including the light-emitting element 100 shown in fig. 1A and 1B and a light source 180 for making excitation light enter the photoluminescent layer 110.

FIG. 17A shows a period p having the x-direction_xA 1-dimensional periodic structure of (a).

FIG. 17B shows a period p having the x-direction_xPeriod p in y-direction_yA 2-dimensional periodic structure of (a).

Fig. 17C is a graph showing the wavelength dependence of the light absorptance of the structure of fig. 17A.

Fig. 17D is a graph showing the wavelength dependence of the absorbance of the structure of fig. 17B.

Fig. 18A is a diagram showing an example of a 2-dimensional periodic structure.

Fig. 18B is a diagram showing another example of the 2-dimensional periodic structure.

Fig. 19A is a diagram showing a modification of the periodic structure formed on the transparent substrate.

Fig. 19B is a diagram showing another modification of the periodic structure formed on the transparent substrate.

Fig. 19C is a diagram showing the result of calculating the degree of enhancement of light output in the front direction by changing the emission wavelength and the period of the periodic structure in the structure of fig. 19A.

Fig. 20 is a diagram showing a structure in which a plurality of powdery light-emitting elements are mixed.

Fig. 21 is a plan view showing an example in which a plurality of periodic structures having different periods are arranged on a photoluminescent layer in 2-dimensions.

Fig. 22 is a diagram showing an example of a light-emitting element having a structure in which a plurality of photoluminescent layers 110 each having an uneven structure formed on a surface thereof are stacked.

Fig. 23 is a cross-sectional view showing an example of a structure in which a protective layer 150 is provided between the photoluminescent layer 110 and the periodic structure 120.

Fig. 24 is a view showing an example in which the periodic structure 120 is formed by processing only a part of the photoluminescent layer 110.

Fig. 25 is a cross-sectional TEM image showing a photoluminescent layer formed on a glass substrate having a periodic structure.

Fig. 26 is a graph showing the results of measuring the spectrum of the emitted light of the light-emitting element manufactured in trial in the front direction.

Fig. 27A is a view showing a state in which a light emitting element that emits linearly polarized light in the TM mode is rotated about an axis parallel to the row direction of the 1-dimensional periodic structure 120 as a rotation axis.

Fig. 27B is a graph showing the results of measuring the angular dependence of the emitted light when the light-emitting element manufactured in trial was rotated as shown in fig. 27A.

Fig. 27C is a graph showing the result of calculating the angular dependence of the emitted light when the light-emitting element manufactured in trial was rotated as shown in fig. 27A.

Fig. 27D is a view showing a state in which the light emitting element that emits linearly polarized light in the TE mode is rotated about an axis parallel to the row direction of the 1-dimensional periodic structure 120 as a rotation axis.

Fig. 27E is a graph showing the results of measuring the angular dependence of the emitted light when the light-emitting element manufactured in trial was rotated as shown in fig. 27D.

Fig. 27F is a graph showing the result of calculating the angular dependence of the emitted light when the light-emitting element manufactured in trial was rotated as shown in fig. 27D.

Fig. 28A is a view showing a state in which a light emitting element that emits linearly polarized light in the TE mode is rotated about an axis perpendicular to the row direction of the 1-dimensional periodic structure 120 as a rotation axis.

Fig. 28B is a graph showing the results of measuring the angular dependence of the emitted light when the light-emitting element manufactured in trial was rotated as shown in fig. 28A.

Fig. 28C is a graph showing the result of calculating the angular dependence of the emitted light when the light-emitting element manufactured in trial was rotated as shown in fig. 28A.

Fig. 28D is a view showing a state in which the light emitting element that emits linearly polarized light in the TM mode is rotated about an axis parallel to the row direction of the 1-dimensional periodic structure 120 as a rotation axis.

Fig. 28E is a graph showing the results of measuring the angular dependence of the emitted light when the light-emitting element manufactured in trial was rotated as shown in fig. 28D.

Fig. 28F is a graph showing the result of calculating the angular dependence of the emitted light when the light-emitting element manufactured in trial was rotated as shown in fig. 28D.

Fig. 29 is a graph showing the results of measuring the angular dependence of the emitted light (wavelength 610nm) of a light-emitting element manufactured in a trial.

Fig. 30 is a perspective view schematically showing an example of a flat plate type waveguide.

Fig. 31 is a schematic diagram illustrating a relationship between a wavelength of light subjected to a light emission enhancement effect and an emission direction of a light-emitting element having the periodic structure 120 on the photoluminescent layer 110.

Fig. 32A is a schematic plan view showing an example of a structure in which a plurality of periodic structures having different wavelengths exhibiting a light emission enhancement effect are arranged.

Fig. 32B is a schematic plan view showing an example of a structure in which a plurality of periodic structures having different orientations in which the convex portions of the 1-dimensional periodic structure extend are arranged.

Fig. 32C is a schematic plan view showing an example of a structure in which a plurality of 2-dimensional periodic structures are arranged.

Fig. 33 is a schematic cross-sectional view of a light-emitting element provided with a microlens.

Fig. 34A is a schematic cross-sectional view of a light-emitting element including a plurality of photoluminescent layers having different emission wavelengths.

Fig. 34B is a schematic cross-sectional view of another light-emitting element including a plurality of photoluminescent layers having different emission wavelengths.

Fig. 35A is a schematic cross-sectional view of a light-emitting element including a diffusion preventing layer (barrier layer) under a photoluminescent layer.

Fig. 35B is a schematic cross-sectional view of a light-emitting element including a diffusion preventing layer (barrier layer) under a photoluminescent layer.

Fig. 35C is a schematic cross-sectional view of a light-emitting element including a diffusion preventing layer (barrier layer) under a photoluminescent layer.

Fig. 35D is a schematic cross-sectional view of a light-emitting element including a diffusion preventing layer (barrier layer) under a photoluminescent layer.

Fig. 36A is a schematic cross-sectional view of a light-emitting element including a crystal growth layer (seed layer) below a photoluminescent layer.

Fig. 36B is a schematic cross-sectional view of a light-emitting element including a crystal growth layer (seed layer) below a photoluminescent layer.

Fig. 36C is a schematic cross-sectional view of a light-emitting element including a crystal growth layer (seed layer) below a photoluminescent layer.

Fig. 37A is a schematic cross-sectional view of a light-emitting element provided with a surface protective layer for protecting a periodic structure.

Fig. 37B is a schematic cross-sectional view of a light-emitting element provided with a surface protective layer for protecting a periodic structure.

Fig. 38A is a schematic cross-sectional view of a light-emitting element provided with a transparent high thermal conductive layer.

Fig. 38B is a schematic cross-sectional view of a light-emitting element provided with a transparent high thermal conductive layer.

Fig. 38C is a schematic cross-sectional view of a light-emitting element provided with a transparent high thermal conductive layer.

Fig. 38D is a schematic cross-sectional view of a light-emitting element provided with a transparent high thermal conductive layer.

Fig. 39 is a graph showing the result of calculating a trigonometric series including terms only 1 time (sine wave), within 3 times, within 5 times, and within 11 times.

Fig. 40 is a schematic cross-sectional view showing a periodic structure in which a plurality of rectangular projections are included in a cross-sectional shape.

Fig. 41A is a schematic cross-sectional view showing a periodic structure in which a plurality of convex portions each having a triangular cross-sectional shape are included.

Fig. 41B is a schematic cross-sectional view showing a periodic structure having a sinusoidal cross-sectional shape.

Fig. 42 is a schematic cross-sectional view showing an example of a cross section of a light-emitting element according to another embodiment of the present invention.

Fig. 43 is a schematic diagram showing a part of a vertical cross section of a periodic structure including a plurality of convex portions Pt.

Fig. 44 is a graph showing the result of calculating the degree of enhancement of light emitted in the front direction by changing the inclination angle of the side surfaces of the plurality of projections in the periodic structure 120 b.

Fig. 45 is a schematic cross-sectional view showing a modification of the light-emitting element in which the periodic structure including the convex portions having the inclined side surfaces is formed on the photoluminescent layer 110.

Fig. 46 is a graph showing the results of calculating the degree of enhancement of light emitted in the front direction by changing the inclination angles of the side surfaces of the plurality of projections in the periodic structure 120b on the photoluminescent layer 110 and the periodic structure 120a on the substrate 140.

Fig. 47 is a graph showing the calculation results when the cross-sectional shape of each of the plurality of projections in the periodic structure 120b on the photoluminescent layer 110 is rectangular and the cross-sectional shape of each of the plurality of projections in the periodic structure 120a on the substrate 140 is trapezoidal.

Fig. 48A is a schematic cross-sectional view showing another example of the cross-sectional shape of the periodic structure.

Fig. 48B is a schematic cross-sectional view showing another example of the cross-sectional shape of the periodic structure.

Fig. 48C is a schematic cross-sectional view showing another example of the cross-sectional shape of the periodic structure.

Fig. 48D is a schematic cross-sectional view showing another example of the cross-sectional shape of the periodic structure.

Fig. 49A is a diagram schematically showing a state where material particles released from the target collide with the surface of the substrate 140 in a case where the pressure during sputtering is relatively low.

Fig. 49B is a diagram schematically showing a state where material particles released from the target collide with the surface of the substrate 140 in a case where the pressure during sputtering is relatively high.

FIG. 50A shows a process for depositing YAG: ce, and a cross-sectional image of the sample.

FIG. 50B shows a case where YAG is deposited by sputtering on a quartz substrate having a periodic structure including a plurality of projections having a rectangular cross-sectional shape and a height of 170 nm: ce, and a cross-sectional image of the sample.

Fig. 51A is a schematic cross-sectional view showing a film of a photoluminescent material obtained in a case where the height of the convex portion in the periodic structure 120a on the substrate 140 is relatively small.

Fig. 51B is a schematic cross-sectional view showing a film of a photoluminescent material obtained in a case where the height of the convex portion in the periodic structure 120a on the substrate 140 is relatively small.

FIG. 51C shows a case where YAG is deposited by sputtering on a quartz substrate having a periodic structure including a plurality of projections having a rectangular cross-sectional shape and a height of 60 nm: ce, and a cross-sectional image of the sample.

Fig. 52A is a schematic cross-sectional view showing a film of a photoluminescent material obtained in a case where the height of the convex portion in the periodic structure 120a on the substrate 140 is relatively large.

Fig. 52B is a schematic cross-sectional view showing a film of a photoluminescent material obtained in a case where the height of the convex portion in the periodic structure 120a on the substrate 140 is relatively large.

FIG. 52C shows a case where YAG: ce, and a cross-sectional image of the sample.

Fig. 53 is a schematic cross-sectional view for explaining an offset amount between the periodic structure 120a and the periodic structure 120 b.

Fig. 54 is a graph showing the results of calculating the degree of enhancement of light emitted in the front direction by changing the amount of shift of the periodic structure 120b with respect to the periodic structure 120 a.

Fig. 55 is a perspective view showing a structure including a member 601 provided with a surface structure including two protrusions on one surface, and a member 602 covering the member 601.

Fig. 56 is a schematic cross-sectional view showing an example of a laminated structure of a member 603 having a surface structure including a plurality of projections Pt and a member 604 covering the member 603.

Fig. 57 is a schematic cross-sectional view showing another example of a laminated structure of a member 603 having a surface structure including a plurality of projections Pt and a member 604 covering the member 603.

Fig. 58 is a schematic cross-sectional view showing an example of a surface structure having at least one of a plurality of convex portions and a plurality of concave portions.

Detailed Description

[1. summary of embodiments of the invention ]

The present invention includes a light-emitting element described in the following items.

[ item 1]

A light-emitting element is provided with: a light transmitting layer; a photoluminescent layer on the light-transmitting layer and emitting light with wavelength λ in air when receiving the excitation light_aThe light of (2); the photoluminescent layer has a 1 st surface structure including a plurality of convex portions on a surface opposite to the light-transmitting layer; the light-transmitting layer has a 2 nd surface structure including a plurality of convex portions corresponding to the plurality of convex portions on a surface on the photoluminescent layer side; the 1 st and 2 nd surface structures limit the wavelength of the light emitted from the photoluminescent layer to λ_aThe pointing angle of the light of (1); the plurality of protrusions in the 1 st surface configuration comprises a 1 st protrusion; in a cross section perpendicular to the photoluminescent layer and parallel to the arrangement direction of the plurality of convex portions in the 1 st surface structure, the width of the base portion of the 1 st convex portion is larger than the width of the top portion.

[ item 2]

The light-emitting element according to item 1, wherein the plurality of projections in the 1 st surface structure have base portions each having a width larger than a width of the top portion.

[ item 3]

The light-emitting element according to item 1 or 2, wherein an inclination angle of a side surface of the plurality of convex portions in the 1 st surface structure is smaller than an inclination angle of a side surface of the plurality of convex portions in the 2 nd surface structure.

[ item 4]

The light-emitting element according to any one of items 1 to 3, wherein the 2 nd surface structure includes a 2 nd convex portion corresponding to the 1 st convex portion; in the cross section, the width of the base of the 1 st projection is smaller than the width of the top of the 2 nd projection.

[ item 5]

The light-emitting element according to any one of items 1 to 3, wherein the 2 nd surface structure includes a 2 nd convex portion corresponding to the 1 st convex portion; in the cross section, the width of the base of the 1 st projection is larger than the width of the top of the 2 nd projection.

[ item 6]

The light-emitting element according to item 1, wherein the plurality of convex portions in the 2 nd surface texture include a 2 nd convex portion corresponding to the 1 st convex portion; in the cross section, the width of the base of the 2 nd projection is larger than the width of the top.

[ item 7]

The light-emitting element according to item 6, wherein the plurality of projections in the 1 st surface structure have base portions each having a width larger than a width of the top portion.

[ item 8]

The light-emitting element according to item 6 or 7, wherein the plurality of projections in the 2 nd surface structure have base portions each having a width larger than a width of the top portion.

[ item 9]

The light-emitting element according to any one of items 6 to 8, wherein at least a part of side surfaces of the plurality of projections in the 1 st surface structure is inclined with respect to a direction perpendicular to the photoluminescent layer; at least a part of the side surfaces of the plurality of projections in the 2 nd surface structure is inclined with respect to the direction perpendicular to the photoluminescent layer.

[ item 10]

The light-emitting element according to any one of items 6 to 9, wherein at least one of a part of side surfaces of the plurality of convex portions in the 1 st surface structure and a part of side surfaces of the plurality of convex portions in the 2 nd surface structure is stepped.

[ item 11]

The light-emitting element according to any one of items 1 to 10, wherein a distance between two adjacent projections in the No. 1 surface structure is D1_intD2 represents the distance between two adjacent protrusions in the 2 nd surface structure_intLet the wavelength of the photoluminescent layer in the air be lambda_aHas a refractive index of n_wav－aThen λ_a/n_wav－a<D1_int<λ_aAnd lambda_a/n_wav－a<D2_int<λ_aThe relationship of (1) holds.

[ item 12]

A light-emitting element is provided with: a light transmitting layer; a photoluminescent layer on the light-transmitting layer and emitting light with wavelength λ in air when receiving the excitation light_aThe light of (2); the photoluminescent layer has a 1 st surface configuration including a plurality of recesses on a surface opposite to the light-transmissive layer; the light-transmitting layer has a 2 nd surface configuration including a plurality of recesses corresponding to the plurality of recesses on the surface on the photoluminescent layer side; the 1 st and 2 nd surface structures limit the wavelength of the light emitted from the photoluminescent layer to λ_aThe pointing angle of the light of (1); the plurality of recesses in the 1 st surface configuration includes a 1 st recess; in a cross section perpendicular to the photoluminescent layer and parallel to the arrangement direction of the plurality of recesses in the 1 st surface structure, the width of the opening of the 1 st recess is larger than the width of the bottom.

[ item 13]

The light-emitting element according to item 12, wherein the plurality of concave portions in the 1 st surface structure have opening portions each having a width larger than a width of the bottom portion.

[ item 14]

The light-emitting element according to item 12 or 13, wherein an inclination angle of a side surface of the plurality of concave portions in the 1 st surface configuration is smaller than an inclination angle of a side surface of the plurality of concave portions in the 2 nd surface configuration.

[ item 15]

The light-emitting element according to any one of items 12 to 14, wherein the 2 nd surface structure includes a 2 nd concave portion corresponding to the 1 st concave portion; in the cross section, the width of the bottom of the 1 st recess is smaller than the width of the opening of the 2 nd recess.

[ item 16]

The light-emitting element according to any one of items 12 to 14, wherein the 2 nd surface structure includes a 2 nd concave portion corresponding to the 1 st concave portion; in the cross section, the width of the bottom of the 1 st recess is larger than the width of the opening of the 2 nd recess.

[ item 17]

The light-emitting element according to item 12, wherein the plurality of recesses in the 2 nd surface configuration include a 2 nd recess corresponding to the 1 st recess; in the cross section, the width of the opening of the 2 nd recess is larger than the width of the bottom.

[ item 18]

The light-emitting element according to item 17, wherein the plurality of concave portions in the 1 st surface structure have opening portions each having a width larger than a width of the bottom portion.

[ item 19]

The light-emitting element according to item 17 or 18, wherein the plurality of concave portions in the 2 nd surface structure have opening portions each having a width larger than a width of the bottom portion.

[ item 20]

The light-emitting element according to any one of items 17 to 19, wherein at least a part of side surfaces of the plurality of concave portions in the 1 st surface structure is inclined with respect to a direction perpendicular to the photoluminescent layer; at least a part of the side surfaces of the plurality of recesses in the 2 nd surface structure is inclined with respect to a direction perpendicular to the photoluminescent layer.

[ item 21]

The light-emitting element according to any one of items 17 to 20, wherein at least one of at least a part of side surfaces of the plurality of recesses in the 1 st surface structure and at least a part of side surfaces of the plurality of recesses in the 2 nd surface structure is stepped.

[ item 22]

The light-emitting element according to any one of items 12 to 21, wherein a distance between two adjacent recesses in the No. 1 surface structure is D1_intD2 represents the distance between two adjacent recesses in the 2 nd surface structure_intLet the wavelength of the photoluminescent layer in the air be lambda_aHas a refractive index of n_wav－aThen λ_a/n_wav－a<D1_int<λ_aAnd lambda_a/n_wav－a<D2_int<λ_aThe relationship of (1) holds.

[ item 23]

The light-emitting element according to item 11 or 22, D1_intAnd D2_intAre equal.

[ item 24]

The light-emitting element according to any one of items 1 to 23, wherein the No. 1 surface structure has at least 1A 1 st cycle configuration; the 2 nd surface texture has at least 12 nd periodic texture; if let at least 1 cycle of the 1 st cycle configuration be p1_aAnd a period of at least 12 nd period structure is p2_aLet the wavelength of the photoluminescent layer in the air be lambda_aHas a refractive index of n_wav－aThen λ_a/n_wav－a<p1_a<λ_aAnd lambda_a/n_wav－a<p2_a<λ_aThe relationship of (1) holds.

[ item 25]

The light-emitting element according to any one of items 1 to 24, wherein the 1 st surface structure and the 2 nd surface structure are formed inside the photoluminescent layer such that a wavelength in air emitted from the photoluminescent layer is λ_aThe intensity of the light of (2) is a maximum analog guided wave mode in a 1 st direction predetermined by the 1 st surface structure and the 2 nd surface structure.

[ item 26]

The light-emitting element according to any one of items 1 to 24, wherein the wavelength in air is λ_aThe intensity of the light of (1) is maximum in a 1 st direction predetermined by the 1 st surface structure and the 2 nd surface structure.

[ item 27]

The light-emitting element according to item 25 or 26, wherein the wavelength in air emitted in the 1 st direction is λ_aIs linearly polarized light.

[ item 28]

The light-emitting element according to any one of items 1 to 27, wherein the wavelength of the light emitted from the photoluminescent layer by the 1 st surface structure and the 2 nd surface structure is λ_aIs limited to less than 15.

[ item 29]

The light-emitting element according to any one of items 1 to 27, wherein the wavelength in air is λ_aIs less than 15 deg. with reference to the 1 st direction of light.

The light-emitting element according to the embodiment of the present invention includes a light-transmitting layer and a photoluminescent layer over the light-transmitting layer. The wavelength of the photoluminescence layer receiving the excitation light and emitting the excitation light in the air is lambda_aOf (2) is detected. The photoluminescent layer is opposite to the light-transmitting layerThe side surface has a 1 st surface texture thereon and the light-transmitting layer has a 2 nd surface texture on the surface on the photoluminescent layer side. The 1 st surface configuration includes a plurality of protrusions, and the 2 nd surface configuration includes a plurality of protrusions corresponding to the plurality of protrusions in the 1 st surface configuration. Alternatively, the 1 st surface configuration includes a plurality of recesses, and the 2 nd surface configuration includes a plurality of recesses corresponding to the plurality of recesses in the 1 st surface configuration. The 1 st and 2 nd surface structures limit the wavelength of the light emitted from the photoluminescent layer to λ_aIs measured.

Wavelength lambda_aFor example, in the wavelength range of visible light (e.g., 380nm or more and 780nm or less). In applications using infrared light, wavelength λ_aThere may be cases exceeding 780 nm. On the other hand, in the use using ultraviolet rays, the wavelength λ_aThere may be less than 380 nm. In the present invention, all electromagnetic waves including infrared rays and ultraviolet rays are expressed as "light" for convenience.

The photoluminescent layer includes a photoluminescent material. The photoluminescent material is a material that emits light when receiving excitation light. The photoluminescent material includes a fluorescent material and a phosphorescent material in a narrow sense, and includes not only an inorganic material but also an organic material (e.g., a pigment) and quantum dots (i.e., semiconductor fine particles). The photoluminescent layer may also comprise a host material (i.e. host material) in addition to the photoluminescent material. The matrix material is, for example, an inorganic material such as glass or oxide, or a resin.

The light transmitting layer may be a substrate supporting the photoluminescent layer. The light-transmitting layer is, for example, arranged close to the photoluminescent layer, and is formed of a material having a high transmittance for light emitted from the photoluminescent layer, for example, an inorganic material or a resin. The light-transmitting layer may be formed of, for example, a dielectric (particularly, an insulator which absorbs light less). When the surface of the photoluminescent layer on the air side has a submicron structure described later, the air layer may be a light-transmitting layer.

A surface structure including at least one of a plurality of convex portions and a plurality of concave portions is formed on a surface of at least one of the photoluminescent layer and the light-transmitting layer. The term "surface" as used herein means a portion (i.e., an interface) which is in contact with another substance. In the case where the light-transmitting layer is a layer of a gas such as air, an interface between the layer of the gas and another substance (for example, a photoluminescent layer) is a surface of the light-transmitting layer. This surface structure may also be referred to as a "concave-convex structure". The surface texture typically includes a portion in which a plurality of projections or a plurality of recesses are periodically arranged one-dimensionally or two-dimensionally. Such surface configurations may be referred to as "periodic configurations". The plurality of convex portions and the plurality of concave portions are formed at the boundary between two members (or media) having different refractive indices and in contact with each other. Thus, the "periodic structure" can be said to be a structure including a portion in which the refractive index periodically shifts in a certain direction. The term "periodicity" as used herein is not limited to a strictly periodic form, but includes a form that is approximately periodic. In the present specification, when the distance between centers (hereinafter, sometimes referred to as "center interval") of two adjacent ones of a plurality of continuous projections or recesses is included in a range within ± 15% of a certain value p with respect to any two adjacent projections or recesses, the portion may be regarded as a periodic structure having a period p.

In the present specification, the "convex portion" refers to a portion that is raised with respect to a portion of the reference height. The "recess" refers to a portion recessed from a portion of the reference height. Fig. 55 shows a structure having a member 601 provided with a surface structure including two protrusions on one surface, and a member 602 covering the member 601. Fig. 55 shows, for reference, x, y, and z axes orthogonal to each other. For convenience of explanation, the x axis, the y axis, and the z axis orthogonal to each other may be shown in other drawings.

The

members

601 and 602 are substantially planar and spread in a plane parallel to the xy plane. In the example shown in fig. 55, the z direction coincides with the direction in which the

members

601 and 602 are stacked, and fig. 55 also schematically shows an xz cross section of the stacked structure of the

members

601 and 602.

In the example shown in fig. 55, the surface structure of the member 601 includes two convex portions Pr1 and Pr2, and the "arrangement direction" of these convex portions can be defined. Similarly, when the surface structure includes two or more recesses, the "arrangement direction" of the recesses may be defined. In the present specification, the "arrangement direction" refers to a direction in which two or more convex portions are arranged or a direction in which two or more concave portions are arranged in a surface structure. As illustrated in fig. 55, when two stripe-shaped projections extending in the y direction are aligned in the x direction, the x direction is the "alignment direction" of the projections. Hereinafter, when a surface structure is formed at the interface between two members at least one of which is planar, a cross section (here, an xz cross section) perpendicular to the planar members and parallel to the arrangement direction in the surface structure may be referred to as a "perpendicular cross section". In this specification, the length measured along the alignment direction in the surface texture is sometimes referred to as "width".

In the example shown in fig. 55, the projections Pr1 and Pr2 are raised in the z direction with respect to the interfaces of the

members

601 and 602. That is, the height reference of the convex portion in this example can be said to be the interface of the

members

601 and 602. In the present specification, in the above-described vertical cross section, a portion of the convex portion at the reference height is referred to as a "base portion" of the convex portion. As schematically shown in fig. 55, for example, the base B1 of the projection Pr1 is a portion of the projection Pr1 that is connected to the reference surface of the bump (here, the interface between the members 601 and 602), and may be a portion of the projection Pr1 that is closest to the interface between the

members

601 and 602. In contrast, in the vertical cross section, a portion of the convex portion where the distance measured from the reference height is largest is referred to as "top portion" of the convex portion. In the illustrated example, the width Bs of the base B1 of the projection Pr1 is equal to the width Tp of the top T1. Hereinafter, the surface connecting the top portion and the base portion may be referred to as a "side surface" of the convex portion. The shape of the side surface in the vertical cross section is not limited to a straight line. The shape of the side surface in the vertical cross section may be curved or stepped.

As will be described in detail later, the shape of the vertical cross section of the convex portion (or concave portion) constituting the surface structure (hereinafter, may be simply referred to as "cross-sectional shape") in the embodiment of the present invention is not limited to the rectangular shape as shown in fig. 55. Fig. 56 and 57 show an example of a cross section of a laminated structure of a member 603 having a surface structure including a plurality of projections Pt and a member 604 covering the member 603. In the example shown in fig. 56, the cross-sectional shape of each convex portion Pt constituting the surface structure is a triangular shape. In this example, the width of the top of the convex portion Pt in the surface structure can be said to be 0. As shown in fig. 57, when the cross-sectional shape of each convex portion Pt constituting the surface structure is a parabolic shape convex upward, the width of the top of the convex portion can be said to be 0. Thus, the width of the top of the convex portion may be 0.

In the vertical cross section of the surface structure illustrated in fig. 56 and 57, when the position of the top of each convex portion Pt is considered as the reference height, the surface structure may be interpreted to include a plurality of concave portions. That is, in the structure illustrated in fig. 56 and 57, the member 603 may have a surface structure including a plurality of recesses Rs. At this time, it can be said that the recessed portion Rs is formed between adjacent two of the portions (the top portions of the respective convex portions Pt in this example) where the reference height is given.

In the present specification, in the above-described vertical cross section, a portion where the distance measured from the reference height is largest among the concave portions constituting the surface structure is referred to as a "bottom portion" of the concave portion. The "bottom" can be said to be the lowest portion in the recess with respect to the reference height. In the example shown in fig. 56 and 57, the width of the bottom Vm of each recess Rs can be said to be 0. As described above, the concave portion in the surface structure is defined by two adjacent ones of the portions giving the reference height. In the present specification, in a vertical cross section, a space between two portions defining a recess is referred to as an "opening" of the recess. An arrow Op in fig. 56 and 57 schematically shows the width of the opening of the recess Rs. The opening portion can be said to connect portions of the surface structure, the height of which decreases from the reference height toward the bottom of the recess. Hereinafter, a surface connecting the opening and the bottom is sometimes referred to as a "side surface" of the recess. Similarly to the convex portion, the shape of the side surface of the concave portion in the vertical cross section may be any of a linear shape, a curved shape, a stepped shape, and an indefinite shape.

Further, depending on the shape, size, and distribution of the convex portions and the concave portions, it may not be easy to determine which of the convex portions and the concave portions is the convex portion. For example, in the cross-sectional view shown in fig. 58, the member 610 may have a concave portion and the member 620 may have a convex portion, or the reverse explanation may be made. In any case, the

members

610 and 620 each have at least one of a plurality of convex portions and concave portions. In the configuration illustrated in fig. 55, it can also be explained that the member 602 has a surface configuration including two concave portions, and in this case, a portion of the member 602 that contacts the top portion T1 described above corresponds to the bottom portion of the concave portion on the left side in fig. 55. At this time, the width of the bottom is Tp, and the width of the opening of the recess is Bs.

The distance between the centers of two adjacent convex portions or two adjacent concave portions in the surface structure (period p in the periodic structure) is typically longer than the wavelength λ in air of the light emitted from the photoluminescent layer_aShort. In the case where light emitted from the photoluminescent layer is visible light, near infrared light of a short wavelength, or ultraviolet light, the distance is shorter than the order of micrometers (i.e., micrometer-sized). Accordingly, such a surface structure is sometimes referred to as a "submicron structure". The "submicron configuration" may also include a portion having a central interval or period exceeding 1 micrometer (μm) in a part. In the following description, a photoluminescent layer that emits visible light is mainly assumed, and a term of "submicron structure" is mainly used as a term representing a surface structure. However, the following discussion is also valid for a surface structure having a microstructure of more than submicron order (for example, a microstructure of micron order used in applications using infrared rays).

In the light-emitting element according to the embodiment of the present invention, as will be described in detail later with reference to the calculation results and the experimental results, a unique electric field distribution is formed at least in the photoluminescent layer. This is formed by the interaction of guided wave light with sub-micron structures, i.e. surface structures. The mode (mode) of light forming such an electric field distribution can be expressed as an "analog guided wave mode". By using this pseudo guided wave mode, as described below, the effects of increasing the luminous efficiency of photoluminescence, improving directivity, and having selectivity for polarized light can be obtained. In the following description, a new structure and/or a new mechanism discovered by the present inventors will be described using terms such as a pseudo guided wave mode. This description is merely an illustrative 1 and is not intended to limit the present invention in any way.

The submicron structure comprises, for example, a plurality of projections, provided that the distance between centers of adjacent projections is D_intThen λ can be satisfied_a/n_wav－a<D_int<λ_aThe relationship (2) of (c). The 1 st surface structure in the photoluminescent layer and the 2 nd surface structure in the light-transmitting layer may satisfy λ_a/n_wav－a<D_int<λ_aThe relationship (2) of (c). The submicron structure may include a plurality of concave portions instead of the plurality of convex portions. That is, the 1 st surface structure and the 2 nd surface structure may include a plurality of concave portions, respectively, and the center-to-center distance D between the adjacent concave portions may be_intIn each of the 1 st surface structure and the 2 nd surface structure, lambda_a/n_wav－a<D_int<λ_aThe relationship of (1) holds. Hereinafter, for simplicity, the submicron structure will be described assuming that it has a plurality of projections. λ represents the wavelength of light, λ_aThe representation is the wavelength of light in air. n is_wavIs the refractive index of the photoluminescent layer. When the photoluminescent layer is a medium in which a plurality of materials are mixed, the average refractive index obtained by weighting the refractive index of each material by the volume ratio thereof is defined as n_wav. Typically the refractive index n depends on the wavelength, so it will preferably be relative to λ_aThe refractive index of light of (a) is explicitly indicated as n_wav－aHowever, this may be omitted for simplicity. n is_wavBasically, the refractive index of the photoluminescent layer is set to n, where the refractive index of the layer adjacent to the photoluminescent layer is larger than the refractive index of the photoluminescent layer, the refractive index of the layer having a larger refractive index and the refractive index of the photoluminescent layer are weighted by the volume ratio of each of the refractive indices_wav. This is because, in this case, it is optically equivalent to the case where the photoluminescent layer is composed of a plurality of layers of different materials.

If the effective refractive index of the medium for light simulating the guided wave mode is set to n_effThen n is satisfied_a<n_eff<n_wav. Here, n is_aIs the refractive index of air. If it is to be simulatedConsidering that light in the guided mode is transmitted while being totally reflected at the incident angle θ inside the photoluminescent layer, the effective refractive index n is_effCan be recorded as n_eff＝n_wavsin θ. Furthermore, due to the effective refractive index n_effSince the refractive index of the medium existing in the region where the electric field of the guided wave mode is distributed depends on the refractive index of the medium, for example, when the sub-micron structure is formed in the light-transmitting layer, the refractive index depends on not only the refractive index of the photoluminescent layer but also the refractive index of the light-transmitting layer. In addition, since the electric field distribution differs according to the polarization direction (TE mode and TM mode) of the analog guided wave mode, the effective refractive index n is different in the TE mode and the TM mode_effMay be different.

The sub-micron structure is formed in at least one of the photoluminescent layer and the light-transmitting layer. When the photoluminescent layer and the light-transmitting layer are in contact with each other, a submicron structure may be formed at an interface between the photoluminescent layer and the light-transmitting layer. In this case, the photoluminescent layer and the light-transmitting layer may have a submicron structure. The light-transmitting layer having a submicron structure may be disposed close to the photoluminescent layer. Here, the light-transmitting layer (or a submicron structure thereof) is close to the photoluminescent layer, and typically means that the distance therebetween is the wavelength λ_aLess than half. Thereby, the electric field of the guided wave mode reaches a submicron structure, and a simulated guided wave mode is formed. However, when the refractive index of the light-transmitting layer is larger than the refractive index of the photoluminescent layer, light reaches the light-transmitting layer even if the above relationship is not satisfied, and therefore the distance between the sub-micron structure of the light-transmitting layer and the photoluminescent layer may exceed the wavelength λ_aHalf of that. In the present specification, when the photoluminescent layer and the light-transmitting layer are in an arrangement relationship such that an electric field of a guided mode reaches a submicron structure to form a pseudo guided mode, they may be correlated with each other.

When the submicron structure satisfies λ as described above_a/n_wav－a<D_int<λ_aIn the case of the relationship (2), in the use using visible light, the feature is given by a size of submicron order. The submicron structure may include at least 1 periodic structure as in the light-emitting element of the embodiment described in detail below, for example. At least 1 cycle if providedPeriod is p_aThen λ_a/n_wav－a<p_a<λ_aThe relationship of (1) holds. That is, the submicron structure may include a distance D between adjacent protrusions_intIs p_aIs a certain periodic structure. Lambda [ alpha ]_a/n_wav－a<p_a<λ_aThe relationship (2) may be established in each of the 1 st surface structure of the photoluminescent layer and the 2 nd surface structure of the light-transmitting layer. The 1 st surface structure and the 2 nd surface structure may each include a plurality of concave portions, and the period p of the center-to-center distance between adjacent concave portions may be_aIn each of the 1 st surface structure and the 2 nd surface structure, λ_a/n_wav－a<p_a<λ_aThe relationship of (1) holds. If the submicron structure includes such a periodic structure, light simulating a guided wave mode repeatedly interacts with the periodic structure while being transmitted, and is diffracted by the submicron structure. This is different from the phenomenon in which light propagating in a free space is diffracted by a periodic structure, and is a phenomenon in which light acts on the periodic structure while being guided (that is, while being totally reflected repeatedly). Therefore, even if the phase shift due to the periodic structure is small (that is, the height of the periodic structure is small), diffraction of light can be caused efficiently.

If the above mechanism is utilized, the light emission efficiency of photoluminescence is increased by the effect of enhancing the electric field by the simulated guided wave mode, and the generated light is coupled with the simulated guided wave mode. The light of the simulated guided mode will be bent by the amount of the diffraction angle specified by the periodic structure in its travel angle. By utilizing this property, light having a specific wavelength can be emitted in a specific direction. That is, the directivity is significantly improved as compared with the case where the periodic structure is not present. Furthermore, the effective refractive index n is in the TE mode and the TM mode_eff(＝n_wavsin θ), high polarization selectivity can be obtained at the same time. For example, as will be described later in the experimental examples, a light-emitting element which strongly emits linearly polarized light (for example, TM mode) having a specific wavelength (for example, 610nm) in the front direction can be obtained. In this case, the angle of directivity of the light emitted in the front direction is, for example, less than 15 °. Here, the "angle of orientation" is definedThe angle between the direction in which the intensity of the emitted linearly polarized light of a specific wavelength is maximum and the direction in which the intensity is 50% of the maximum intensity is defined. That is, the pointing angle is an angle on one side when the direction in which the strength is the maximum is set to 0 °. Thus, the periodic structure (i.e., surface structure) of the embodiments of the present invention limits the specific wavelength λ_aIs measured. In other words, let the wavelength λ_aThe distribution of the light of (2) is a narrower angle than that in the case where the periodic structure is not provided. Such a light distribution in which the directivity angle is reduced as compared with the case where the periodic structure is not present is sometimes referred to as "narrow-angle light distribution". Periodic structure limiting wavelength λ of embodiments of the present invention_aBut not the wavelength λ_aAll of the light of (a) is emitted at a narrow angle. For example, in an example shown in fig. 29 described later, the wavelength λ is also present in a direction of an angle (for example, 20 ° to 70 °) deviating from a direction in which the intensity is maximum_aSlightly emitted. However, the wavelength λ as a whole_aThe emitted light is concentrated in the range of 0 to 20 degrees, and the pointing angle is limited.

In addition, unlike a normal diffraction grating, the periodic structure of the exemplary embodiment of the present invention has a specific light wavelength λ_aShort cycle time. As a result, light of a specific wavelength is split into a plurality of diffracted lights such as 0 th order light (i.e., transmitted light) and ± 1 st order diffracted light, and is emitted. Such a diffraction grating generates high-order diffracted light on both sides of the 0 th-order light. The high-order diffracted light generated on both sides of the 0 th order light of the diffraction grating makes it difficult to realize narrow-angle light distribution. In other words, the conventional diffraction grating does not exhibit the effect unique to the embodiment of the present invention of limiting the light directivity angle to a predetermined angle (for example, about 15 °). In this regard, the periodic structure according to the embodiment of the present invention has a property significantly different from that of a conventional diffraction grating.

If the periodicity of the submicron structure is low, the directivity, the light emission efficiency, the polarization degree, and the wavelength selectivity become weak. It is sufficient to adjust the periodicity of the submicron structure as needed. The periodic structure may be a 1-dimensional periodic structure in which the selectivity of polarized light is high, or may be a 2-dimensional periodic structure in which the degree of polarization can be reduced.

The sub-micron configuration may include a plurality of periodic configurations. The plurality of periodic configurations, for example, periods (pitches) are different from each other. Alternatively, in the plurality of periodic configurations, for example, directions (axes) having the periodicity are different from each other. The plurality of periodic structures may be formed in the same plane or may be stacked. Of course, the light-emitting element may have a plurality of photoluminescent layers and a plurality of light-transmitting layers having a plurality of submicron structures.

The submicron structure can be used not only to control light emitted from the photoluminescent layer but also to guide excitation light to the photoluminescent layer with good efficiency. That is, the excitation light is diffracted by the submicron structure and coupled to the analog guided mode guided in the photoluminescent layer and the light-transmitting layer, whereby the photoluminescent layer can be excited efficiently. If the wavelength of the light for exciting the photoluminescent material in the air is set to be lambda_exLet the refractive index of the photoluminescent layer for the excitation light be n_wav－exThen only use λ_ex/n_wav－ex<D_int<λ_exA submicron structure in which the relationship of (1) is established is sufficient. n is_wav－exIs the refractive index at the excitation wavelength of the photoluminescent material. If the period is set to p_exThen a signal with λ may also be used_ex/n_wav－ex<p_ex<λ_exA submicron structure having a periodic structure in which the relationship (1) holds. Wavelength lambda of the excitation light_exFor example 450nm, but may also be a shorter wavelength than visible light. When the wavelength of the excitation light is in the visible light range, the excitation light may be emitted together with the light emitted from the photoluminescent layer.

[2. knowledge as the basis of the present invention ]

Before describing specific embodiments of the present invention, the understanding that underlies the present invention will be described first. As described above, photoluminescent materials used in fluorescent lamps, white LEDs, and the like emit light isotropically. In order to irradiate a specific direction with light, an optical member such as a reflector or a lens is required. However, if the photoluminescent layer itself emits light with directivity, the optical member as described above is not necessary (or can be made small). This enables the size of the optical device and the instrument to be significantly reduced. Based on such an assumption, the present inventors have studied the structure of the photoluminescent layer in detail in order to obtain directional light emission.

The present inventors first considered that the light emitted from the photoluminescent layer has a specific directivity in order to deflect the light in a specific direction. The light emission ratio (rate) Γ, which is an index for characterizing light emission, is expressed by the following formula (1) according to the gold law of fermi.

[ numerical formula 1]

In the formula (1), r is a vector indicating a position, λ is a wavelength of light, d is a dipole vector (dipole vector), E is an electric field vector, and ρ is a state density. In most of the substances, except for a part of crystalline substances, the dipole vector d has random directivity. In addition, when the size and thickness of the photoluminescent layer are sufficiently larger than the wavelength of light, the magnitude of the electric field E is also substantially constant regardless of the orientation. In this way, in almost all cases,<(d·E(r))>²the value of (d) does not depend on the direction. That is, the light emission ratio Γ is constant regardless of the direction. Therefore, in almost all cases, the photoluminescent layer emits light isotropically.

On the other hand, according to the formula (1), in order to obtain anisotropic light emission, careful design is required such that the dipole vector d is aligned with a specific direction or the component in the specific direction of the electric field vector is increased. By elaborating one of the two, directional light emission can be realized. In the embodiment of the present invention, the effect of blocking light toward the photoluminescent layer is utilized to utilize the analog guided wave mode in which the electric field component in a specific direction is enhanced. The results of a study and detailed analysis of the structure used for this are described below.

[3. Structure for intensifying electric field in specific direction ]

The inventors of the present invention considered to control light emission using a guided wave mode having a strong electric field. By making the structure in which the waveguide structure itself includes the photoluminescent material, the generated light can be coupled to the guided mode. However, when the waveguide structure is formed using only the photoluminescent material, the emitted light is in the waveguide mode, and therefore, the light hardly comes out in the front direction. Therefore, the inventors of the present invention considered to combine a waveguide including a photoluminescent material with a periodic structure. When the periodic structure is close to the waveguide and the electric field of light is guided while overlapping the periodic structure, the analog guided mode exists by the action of the periodic structure. That is, the analog guided wave mode is a guided wave mode limited by a periodic structure, and is characterized in that an antinode of an electric field amplitude occurs at the same period as that of the periodic structure. The mode is a mode in which an electric field in a specific direction is enhanced by light being confined in a waveguide structure. Further, since the mode interacts with the periodic structure to convert the propagation light in a specific direction by a diffraction effect, the light can be emitted to the outside of the waveguide. Further, since light other than the analog guided mode is less effectively confined in the waveguide, the electric field is not enhanced. Thereby, almost all of the emitted light is coupled to the analog guided wave mode having a large electric field component.

That is, the inventors of the present invention considered that a light source having directivity is realized by configuring a waveguide including a photoluminescent layer (or a waveguide including a photoluminescent layer) containing a photoluminescent material to be close to a periodic structure and coupling generated light to an analog waveguide mode converted into propagating light in a specific direction.

As a simple structure of the waveguide structure, a flat waveguide is focused. The slab (slab) type waveguide is a waveguide in which a light guiding portion has a slab structure. Fig. 30 is a perspective view schematically showing an example of the plate-shaped waveguide 110S. When the refractive index of the waveguide 110S is higher than the refractive index of the transparent substrate 140 supporting the waveguide 110S, there is a mode of light propagating in the waveguide 110S. By configuring such a flat waveguide to include a photoluminescent layer, the electric field of light generated from the light-emitting point and the electric field of the guided mode largely overlap with each other, and therefore most of the light generated in the photoluminescent layer can be coupled to the guided mode. Further, by making the thickness of the photoluminescent layer to be about the wavelength of light, it is possible to form a state in which only a guided wave mode having a large electric field amplitude exists.

Further, when the periodic structure is close to the photoluminescent layer, an electric field of the guided wave mode interacts with the periodic structure to form an analog guided wave mode. In the case where the photoluminescent layer is composed of a plurality of layers, the analog guided mode is formed as long as the electric field of the guided mode has a periodic structure. It is not necessary that the entire photoluminescent layer be a photoluminescent material, as long as at least a part of the region thereof has a function of emitting light.

When the periodic structure is formed of a metal, a guided wave mode and a mode based on the effect of plasmon resonance (plasmon resonance) are formed. This mode has different properties from the analog guided wave mode described above. Further, since the absorption of the mode by the metal is large, the loss becomes large, and the effect of enhancing the light emission becomes small. Therefore, as the periodic structure, it is preferable to use a dielectric having less absorption.

The inventors of the present invention first studied the coupling of the generated light with the pseudo guided mode that can be emitted as propagating light in a specific angular direction by forming a periodic structure on the surface of such a guided wave channel. Fig. 1A is a perspective view schematically showing an example of a light-emitting element 100 including such a waveguide (for example, a photoluminescent layer) 110 and a periodic structure (for example, a part of a light-transmitting layer) 120. Hereinafter, when the light-transmitting layer has a periodic structure (that is, when a periodic submicron structure is formed in the light-transmitting layer), the periodic structure 120 may be referred to as the light-transmitting layer 120. In this example, the periodic structure 120 is a 1-dimensional periodic structure in which a plurality of stripe-shaped projections extending in the y direction are arranged at equal intervals in the x direction. Fig. 1B is a cross-sectional view of the light-emitting element 100 cut along a plane parallel to the xz plane. If the periodic structure 120 of the period p is provided in contact with the waveguide 110, the wave number k in the in-plane direction is obtained_wavThe wave number k of the analog guided wave mode of (2) is converted by the propagation light outside the guided wave path_outCan be used as followsThe formula (2).

[ numerical formula 2]

M in the formula (2) is an integer and represents the number of diffraction orders.

Here, for simplicity, the light guided in the waveguide is approximately considered to be at an angle θ_wavThe following equations (3) and (4) hold for the propagating light.

[ numerical formula 3]

[ numerical formula 4]

In these formulae, λ₀Is the wavelength of light in air, n_wavIs the refractive index of the waveguide, n_outIs the refractive index of the medium on the emission side, theta_outIs an emission angle when light is emitted to a substrate or air outside the waveguide. The injection angle θ is expressed by the expressions (2) to (4)_outThis can be represented by the following formula (5).

[ numerical formula 5]

n_outsinθ_out＝n_wavsinθ_wav-mλ₀/p (5)

According to the formula (5), when n is_wavsinθ_wav＝mλ₀When/p is established, is θ_outWhen the wavelength is 0, the light can be emitted in a direction perpendicular to the surface of the waveguide (i.e., front surface).

Based on the above principle, it is considered that strong light can be emitted in the direction by coupling the generated light with a specific analog guided wave mode and converting the coupled light into light at a specific emission angle by a periodic structure.

There are some constraints to achieve the above situation. First, in order for the analog guided mode to exist, the light propagating in the guided wave path needs to be totally reflected. The conditions used for this are represented by the following formula (6).

[ numerical formula 6]

n_out＜n_wavsinθ_wav(6)

In order to diffract the pseudo guided mode by the periodic structure and emit light to the outside of the waveguide, it is necessary that the value of-1 is given to equation (5)<sinθ_out<1. Thus, the following formula (7) needs to be satisfied.

[ number formula 7]

In contrast, it is understood that if equation (6) is considered, equation (8) below may be satisfied.

[ number formula 8]

Further, the direction of the light emitted from the waveguide 110 is made to be a front direction (θ)_outAs is clear from formula (5) ═ 0), the following formula (9) is required.

[ numerical formula 9]

p＝mλ₀/(n_wavsinθ_wav) (9)

From the formulae (9) and (6), the following formula (10) is required.

[ numerical formula 10]

In addition, when the periodic structure as shown in fig. 1A and 1B is provided, since the diffraction efficiency of a high order in which m is 2 or more is low, the design can be made focusing mainly on 1 st order diffracted light in which m is 1. Therefore, in the periodic structure of the present embodiment, assuming that m is 1, the period p is determined so as to satisfy the following expression (11) obtained by modifying the expression (10).

[ numerical formula 11]

As shown in FIGS. 1A and 1B, when the waveguide (photoluminescent layer) 110 is not in contact with the transparent substrate, n is a factor_outSince the refractive index of air is (about 1.0), the period p may be determined so as to satisfy the following expression (12).

[ numerical formula 12]

On the other hand, a structure in which the photoluminescent layer 110 and the periodic structure 120 are formed on the transparent substrate 140 as illustrated in fig. 1C and 1D may be employed. In this case, the refractive index n of the transparent substrate 140 is increased_sSince the refractive index is larger than that of air, the period p is determined so as to satisfy the condition that n is represented by the formula (11)_out＝n_sThe following formula (13).

[ numerical formula 13]

In equations (12) and (13), although the case where m is 1 in equation (10) is assumed, m ≧ 2 may be employed. That is, when both surfaces of the light-emitting element 100 are in contact with an air layer as shown in fig. 1A and 1B, m may be an integer of 1 or more and the period p may be set so as to satisfy the following expression (14).

[ numerical formula 14]

Similarly, in the case where the photoluminescent layer 110 is formed on the transparent substrate 140 as in the light-emitting element 100a shown in fig. 1C and 1D, the period p may be set so as to satisfy the following expression (15).

[ numerical formula 15]

By determining the period p of the periodic structure so as to satisfy the above inequality, light generated from the photoluminescent layer 110 can be emitted in the front direction, and therefore a light-emitting device having directivity can be realized.

[4. verification based on calculation ]

[ 4-1. period, wavelength dependence ]

The inventors of the present invention verified that the above-described light emission in a specific direction can be actually realized by optical analysis. The optical analysis was performed by calculation using diffactmod manufactured by "サイバネット" corporation. In these calculations, when light is made to enter the light-emitting element perpendicularly from the outside, the degree of enhancement of light emitted perpendicularly to the outside is determined by calculating the increase or decrease in the absorption of light in the photoluminescent layer. The process of coupling light incident from the outside to the simulated guided wave mode and absorbing the light in the photoluminescent layer corresponds to the reverse process of calculating the coupling of light emitted in the photoluminescent layer to the simulated guided wave mode and converting the light into propagating light emitted perpendicularly to the outside. In addition, in the calculation of the electric field distribution of the analog guided wave mode, the electric field in the case where light enters from the outside is calculated similarly.

FIG. 2 shows that the thickness of the photoluminescent layer is 1 μm and the refractive index of the photoluminescent layer is n_wavThe intensity of light emitted in the front direction was calculated by changing the emission wavelength and the period of the periodic structure, respectively, to 1.8, the height of the periodic structure was 50nm, the refractive index of the periodic structure was 1.5. As shown in fig. 1A, the calculation model is calculated assuming that the 1-dimensional periodic structure is uniform in the y direction and the polarized light of the light is a TM mode having an electric field component parallel to the y direction. As can be seen from the results of fig. 2, the peak of the degree of enhancement exists at a specific combination of wavelength and period. In fig. 2, the magnitude of the enhancement degree is represented by the shade of the color, and the enhancement degree is larger for darker (i.e., darker) and smaller for lighter (i.e., whiter).

In the above calculation, it is assumed that the cross section of the periodic structure is a rectangle as shown in fig. 1B. Fig. 3 shows a graph illustrating conditions under which m is 1 and m is 3 in formula (10). As can be seen from a comparison of fig. 2 and 3, the peak positions in fig. 2 exist at positions corresponding to m 1 and m 3. The reason why the intensity is strong when m is 1 is that the diffraction efficiency of the 1 st order diffracted light is higher than that of the 3 rd or higher order diffracted light. The absence of the peak with m 2 is due to the lower diffraction efficiency of the periodic structure.

It can be confirmed that a plurality of lines (lines) exist in fig. 2 in regions corresponding to m-1 and m-3 shown in fig. 3, respectively. This is considered because there are a plurality of analog guided wave modes.

[ 4-2. thickness dependence ]

FIG. 4 shows the refractive index n of the photoluminescent layer_wavThe periodic structure had a period of 400nm, a height of 50nm, and a refractive index of 1.5, and the degree of enhancement of light output in the front direction was calculated by changing the light emission wavelength and the thickness t of the photoluminescent layer as shown in fig. 1.8. It is known that the light enhancement degree reaches a peak value when the thickness t of the photoluminescent layer is a specific value.

Fig. 5A and 5B show the results of calculating the electric field distribution of the mode guided in the x direction at the wavelength 600nm, thickness t 238nm, and thickness 539nm, respectively, at which the peak is present in fig. 4. For comparison, fig. 5C shows the same calculation result for the case where t is 300nm where no peak exists. The calculation model assumes a 1-dimensional periodic structure uniform in the y direction, as described above. In each figure, a darker area indicates a higher electric field strength, and a whiter area indicates a lower electric field strength. When t is 238nm or 539nm, the electric field intensity distribution is high, whereas when t is 300nm, the electric field intensity is low as a whole. This is because, when t is 238nm or 539nm, a guided wave mode exists, and light is strongly confined. Further, the convex portion or a portion (antinode) directly below the convex portion is always the strongest electric field, and the characteristic of the electric field having a correlation with the periodic structure 120 is observed. That is, it is understood that the mode of the guided wave is obtained according to the arrangement of the periodic structure 120. In addition, comparing the case where t is 238nm with the case where t is 539nm, it is found that the number of nodes (white portions) of the electric field in the z direction differs by only 1 mode.

[ 4-3. dependence of polarized light ]

Next, in order to confirm the polarization dependence, the degree of enhancement of light was calculated in the case where the polarized light of light is the TE mode having an electric field component perpendicular to the y direction under the same conditions as in the calculation of fig. 2. The result of this calculation is shown in fig. 6. Although the peak position slightly changes compared to the TM mode (fig. 2), the peak position is included in the region shown in fig. 3. This confirms that the structure of the present embodiment is effective for both TM mode and TE mode polarized light.

[ 4-4.2 dimensional periodic Structure ]

Further, the effect of the periodic structure in 2 dimensions was investigated. Fig. 7A is a plan view showing a part of a 2-dimensional periodic structure 120' in which concave portions and convex portions are arranged in both the x direction and the y direction. The darker areas in the figure represent the convex portions, and the whiter areas represent the concave portions. In such a 2-dimensional periodic structure, diffraction in both the x-direction and the y-direction needs to be considered. Diffraction in only the x direction or only the y direction is the same as in the 1-dimensional case, but since there is also diffraction in a direction having both x and y components (for example, a 45 ° oblique direction), it is expected that a result different from that in the 1-dimensional case can be obtained. The result of calculating the degree of enhancement of light with respect to such a 2-dimensional periodic configuration is shown in fig. 7B. The calculation conditions other than the periodic structure are the same as those of fig. 2. As shown in fig. 7B, in addition to the peak position of the TM mode shown in fig. 2, a peak position that matches the peak position of the TE mode shown in fig. 6 was observed. This result indicates that the TE mode is also transformed by diffraction and output by the 2-dimensional periodic structure. In the 2-dimensional periodic structure, it is necessary to consider diffraction satisfying the diffraction condition of 1 st order for both the x direction and the y direction. Such diffracted light is √ 2 times (i.e., 2) the period p^1/2Multiple times) of the period of the light beam. From this, it is conceivable that peaks occur with a period √ 2 times the period p, in addition to peaks in the case of the 1-dimensional periodic structure. In fig. 7B, such a peak can also be confirmed.

The 2-dimensional periodic structure is not limited to the square lattice structure having equal periods in the x direction and the y direction as shown in fig. 7A, and may be a lattice structure in which hexagons or triangles are arranged as shown in fig. 18A and 18B. Further, the structure may be such that the periods are different depending on the azimuth direction (for example, the x direction and the y direction in the case of a square grid).

As described above, in the present embodiment, it was confirmed that light in a characteristic pseudo guided wave mode formed by the periodic structure and the photoluminescent layer can be selectively emitted only in the front direction by utilizing the diffraction phenomenon of the periodic structure. In such a structure, the photoluminescent layer is excited by excitation light such as ultraviolet light or blue light, whereby light emission having directivity can be obtained.

[ 5] study of periodic Structure and Structure of photoluminescent layer ]

Next, effects when various conditions such as the periodic structure, the structure of the photoluminescent layer, and the refractive index are changed will be described.

[ 5-1. refractive index of periodic Structure ]

First, studies were made on the refractive index of the periodic structure. The thickness of the photoluminescent layer is 200nm, and the refractive index of the photoluminescent layer is n_wavThe periodic structure was calculated assuming that the polarized light of light is a TM mode having an electric field component parallel to the y direction, and the periodic structure was a 1-dimensional periodic structure uniform in the y direction as shown in fig. 1A, the height was 50nm, and the period was 400 nm. Fig. 8 shows the results of calculating the degree of enhancement of light output in the front direction by changing the emission wavelength and the refractive index of the periodic structure. Fig. 9 shows the results obtained when the thickness of the photoluminescent layer was set to 1000nm under the same conditions.

First, focusing on the film thickness of the photoluminescent layer, it is found that the shift of the wavelength (referred to as peak wavelength) at which the light intensity is a peak against the change in the refractive index of the periodic structure is small in the case of the film thickness of 1000nm (fig. 9) as compared with the case of the film thickness of 200nm (fig. 8). This is because the smaller the thickness of the photoluminescent layer is, the more easily the analog guided wave mode is affected by the refractive index of the periodic structure. That is, the higher the refractive index of the periodic structure is, the larger the effective refractive index is, and accordingly, the peak wavelength is shifted to the longer wavelength side, and the smaller the film thickness is, the more significant the influence thereof is. In addition, the effective refractive index is determined by the refractive index of the medium existing in the region simulating the electric field distribution of the guided wave mode.

Next, focusing on the change in the peak value with respect to the change in the refractive index of the periodic structure, it is found that the peak value spreads and the intensity decreases as the refractive index increases. This is because the higher the refractive index of the periodic structure is, the higher the rate (rate) of releasing light in the analog waveguide mode to the outside is, and therefore, the effect of blocking light is reduced, that is, the lower the Q value is. In order to keep the peak intensity high, it is sufficient to have a structure in which light is appropriately emitted to the outside by using a simulated guided wave mode having a high light confinement effect (i.e., a high Q value). In order to achieve this, it is known that it is not preferable to use a material having a refractive index that is too large compared to the refractive index of the photoluminescent layer for the periodic structure. Therefore, in order to increase the peak intensity and the Q value to some extent, the refractive index of the dielectric (i.e., the light-transmitting layer) constituting the periodic structure may be equal to or less than the refractive index of the photoluminescent layer. The same applies when the photoluminescent layer contains a material other than the photoluminescent material.

[ 5-2. height of periodic Structure ]

Next, a study was made regarding the height of the periodic structure. The thickness of the photoluminescent layer is 1000nm, and the refractive index of the photoluminescent layer is n_wavThe periodic structure is a 1-dimensional periodic structure uniform in the y direction as shown in fig. 1A, and the refractive index is n_pThe calculation was performed assuming that the polarized light of light is a TM mode having an electric field component parallel to the y direction, with a period of 400nm of 1.5. Fig. 10 shows the results of calculating the degree of enhancement of light output in the front direction by changing the emission wavelength and the height of the periodic structure. FIG. 11 shows that the refractive index of the periodic structure is n under the same conditions_pThe calculation result in the case of 2.0. While the peak intensity and Q value (i.e., the line width of the peak) do not change at a height of a certain degree or more in the results shown in fig. 10, it is clear that the peak intensity and Q value decrease as the height of the periodic structure increases in the results shown in fig. 11. This is because the refractive index n in the photoluminescent layer_wavRefraction of specific periodic structureRate n_pIn the high case (fig. 10), the light is totally reflected, so only the evanescent portion of the electric field simulating the guided mode interacts with the periodic structure. The influence of the interaction of the evanescent portion of the electric field with the periodic structure is constant even if the height is further changed in the case where the height of the periodic structure is sufficiently large. On the other hand, the refractive index n in the photoluminescent layer_wavRefractive index n of specific periodic structure_pIn the case of a low level (fig. 11), the light reaches the surface of the periodic structure without being totally reflected, and therefore the height of the periodic structure is more affected. It can be seen from an examination of FIG. 11 that the height is sufficient to be about 100nm, and that the peak intensity and Q value are lowered in a region exceeding 150 nm. Thus, the refractive index n in the photoluminescent layer_wavRefractive index n of specific periodic structure_pWhen the peak intensity is low, the height of the periodic structure may be set to 150nm or less in order to increase the peak intensity and the Q value to some extent.

[ 5-3. polarized light Direction ]

Next, the polarization direction was investigated. Fig. 12 shows the results of calculations assuming that the polarization of light is the TE mode having an electric field component perpendicular to the y direction under the same conditions as the calculations shown in fig. 9. In the TE mode, the electric field in the analog guided wave mode is more likely to leak than in the TM mode, and therefore is susceptible to the influence of the periodic structure. Thereby, the refractive index n in the periodic structure_pRefractive index n of the photoluminescent layer_wavIn a large region, the peak intensity and Q value decrease more significantly than in the TM mode.

[ 5-4. refractive index of photoluminescent layer ]

Next, the refractive index of the photoluminescent layer was investigated. FIG. 13 shows the refractive index n of the photoluminescent layer under the same conditions as the calculation shown in FIG. 9_wavThe case of the change to 1.5. The refractive index n in the photoluminescent layer is known_wavThe case of 1.5 also provides substantially the same effect as that of fig. 9. However, it is known that light having a wavelength of 600nm or more is not emitted in the front direction. This is because λ is expressed by the formula (10)₀<n_wav×p/m＝1.5×400nm/1＝600nm。

From the above analysis, it is found that when the refractive index of the periodic structure is equal to or less than the refractive index of the photoluminescent layer, or the refractive index of the periodic structure is equal to or more than the refractive index of the photoluminescent layer, the peak intensity and the Q value can be increased if the height is 150nm or less.

[6. modification ]

Next, a modified example of the present embodiment will be described.

[ 6-1. Structure having substrate ]

As described above, the light-emitting element may have a structure in which the photoluminescent layer 110 and the periodic structure 120 are formed on the transparent substrate 140, as shown in fig. 1C and 1D. In order to produce such a light-emitting element 100a, a method may be considered in which a thin film is formed on the transparent substrate 140 using a photoluminescent material (including a host material if necessary, the same applies hereinafter) constituting the photoluminescent layer 110, and the periodic structure 120 is formed thereon. In such a structure, the refractive index n of the transparent substrate 140 is such that the photoluminescent layer 110 and the periodic structure 120 have a function of emitting light in a specific direction_sThe refractive index n of the photoluminescent layer is required_wavThe following. When the transparent substrate 140 is provided in contact with the photoluminescent layer 110, the period p needs to be set so as to satisfy the refractive index n of the medium to be emitted in the formula (10)_outIs set to n_sThe formula (15).

To confirm this, the calculation was performed in the case where the photoluminescent layer 110 and the periodic structure 120 under the same conditions as the calculation shown in fig. 2 were provided on the transparent substrate 140 having the refractive index of 1.5. The result of this calculation is shown in fig. 14. It is understood that the peak of the light intensity occurred in a specific cycle can be confirmed for each wavelength as in the result of fig. 2, but the range of the cycle in which the peak occurred is different from the result of fig. 2. In contrast, fig. 15 shows that the condition of expression (10) is n_out＝n_sThe condition of the formula (15). It is understood that in fig. 14, a peak of light intensity appears in a region corresponding to the range shown in fig. 15.

Therefore, in the light-emitting element 100a in which the photoluminescent layer 110 and the periodic structure 120 are provided on the transparent substrate 140, an effect can be obtained in the range of the period p satisfying the formula (15), and a particularly significant effect can be obtained in the range of the period p satisfying the formula (13).

[ 6-2 ] light-emitting device having excitation light source ]

Fig. 16 is a diagram showing a configuration example of a light-emitting device 200 including the light-emitting element 100 shown in fig. 1A and 1B and a light source 180 for making excitation light enter the photoluminescent layer 110. As described above, in the configuration of the present invention, the photoluminescent layer is excited by excitation light such as ultraviolet light or blue light, whereby light emission having directivity can be obtained. By providing the light source 180 configured to emit such excitation light, the light emitting device 200 having directivity can be realized. The wavelength of the excitation light emitted from the light source 180 is typically a wavelength in the ultraviolet or blue region, but is not limited thereto, and is appropriately determined according to the photoluminescent material constituting the photoluminescent layer 110. In fig. 16, the light source 180 is arranged to make excitation light enter from the lower surface of the photoluminescent layer 110, but the arrangement is not limited to such an example, and for example, excitation light may be made to enter from the upper surface of the photoluminescent layer 110. The excitation light may be incident from a direction (i.e., oblique direction) oblique to a direction perpendicular to a main surface (i.e., upper surface or lower surface) of the photoluminescent layer 110. By making the excitation light enter obliquely at an angle at which total reflection occurs in the photoluminescent layer 110, light can be emitted more efficiently.

There is also a method of efficiently emitting light by coupling excitation light and an analog guided wave mode. Fig. 17A to 17D are diagrams for explaining such a method. In this example, the photoluminescent layer 110 and the periodic structure 120 are formed on the transparent substrate 140, similarly to the structures shown in fig. 1C and 1D. First, as shown in fig. 17A, the period p in the x direction is determined for light emission enhancement_xThen, as shown in fig. 17B, the period p in the y direction is determined so that the excitation light is coupled to the analog guided mode_y. Determining the period p_xSo that it satisfies the substitution of p for p in the formula (10)_xThe conditions of (1). On the other hand, let m be an integer of 1 or more and let the wavelength of the excitation light be λ_exIn the medium in contact with the photoluminescent layer 110 exceptThe medium having the highest refractive index other than the periodic structure 120 has a refractive index n_outDetermining the period p_ySo that it satisfies the following formula (16).

[ number formula 16]

Here, n is_outN of the transparent substrate 140 in the example of FIG. 17B_sHowever, in the structure in which the transparent substrate 140 is not provided as in fig. 16, the refractive index of air is (about 1.0).

In particular, if m is 1, the period p is determined_yIf the following expression (17) is satisfied, the effect of converting the excitation light into the analog guided wave mode can be further improved.

[ number formula 17]

Thus, by setting the period p_yThe excitation light can be converted into an analog guided wave mode under the condition that the formula (16) is satisfied (particularly, under the condition that the formula (17) is satisfied). As a result, the photoluminescent layer 110 can be made to efficiently absorb the wavelength λ_exThe excitation light of (1).

Fig. 17C and 17D are graphs showing the results of calculating the ratio of light absorbed when light is incident on the structures shown in fig. 17A and 17B for each wavelength, respectively. In this calculation, let p_x＝365nm，p_y265nm, the light emission wavelength λ from the photoluminescent layer 110 is about 600nm, and the wavelength λ of the excitation light is set to be_exAbout 450nm, and the attenuation coefficient of the photoluminescent layer 110 is 0.003. As shown in fig. 17D, the light generated from the photoluminescent layer 110 exhibits a high absorptance with respect to light of about 450nm as excitation light. This is because the incident light is efficiently converted into an analog guided wave mode, and the rate of absorption by the photoluminescent layer can be increased. Further, the absorption rate increases also for about 600nm, which is the emission wavelength, which means that when light having a wavelength of about 600nm is incident on the structure, it is converted effectively similarlyTo simulate guided wave modes. As described above, the periodic structure 120 shown in fig. 17B is a 2-dimensional periodic structure having structures (referred to as periodic components) having different periods in the x direction and the y direction, respectively. In this way, by using the 2-dimensional periodic structure having a plurality of periodic components, the excitation efficiency can be improved and the emission intensity can be improved. In fig. 17A and 17B, the excitation light is made incident from the substrate 140 side, but the same effect can be obtained if the excitation light is made incident from the periodic structure 120 side.

Further, as a 2-dimensional periodic structure having a plurality of periodic components, a structure as shown in fig. 18A or 18B may be employed. By adopting a structure in which a plurality of projections or recesses having a hexagonal planar shape are periodically arranged as shown in fig. 18A, or a structure in which a plurality of projections or recesses having a triangular planar shape are periodically arranged as shown in fig. 18B, a plurality of main axes (axes 1 to 3 in the drawing) that can be regarded as a period can be determined. Therefore, different periods can be allocated to the respective axial directions. These periods may be set to improve the directivity of light of a plurality of wavelengths, or may be set to achieve good absorption of excitation light. In either case, each cycle is set so as to satisfy the condition corresponding to expression (10).

[ 6-3. periodic Structure on transparent substrate ]

As shown in fig. 19A and 19B, the periodic structure 120a may be formed on the transparent substrate 140, and the photoluminescent layer 110 may be provided thereon. In the configuration example of fig. 19A, the photoluminescent layer 110 is formed so as to follow the periodic structure 120a formed of the irregularities on the substrate 140. As a result, the periodic structure 120b of the same period is also formed on the surface of the photoluminescent layer 110. On the other hand, in the configuration example of fig. 19B, the surface of the photoluminescent layer 110 is processed to be flat. In these configuration examples as well, directional light emission can be realized by setting the period p of the periodic structure 120a so as to satisfy the formula (15).

To verify this effect, in the structure of fig. 19A, the enhancement degree of light output in the front direction was calculated by changing the emission wavelength and the period of the periodic structure. Here, the thickness of the photoluminescent layer 110 is 1000nm, and the refractive index of the photoluminescent layer 110Is n_wavWhen the periodic structure 120a is a 1-dimensional periodic structure uniform in the y direction, the height is 50nm, and the refractive index is n, 1.8_p1.5 with a period of 400nm, assuming that the polarized light of the light is a TM mode with an electric field component parallel to the y direction. The result of this calculation is shown in fig. 19C. In this calculation, the peak of the light intensity was also observed at a cycle satisfying the condition of equation (15).

[ 6-4. powder ]

According to the above embodiments, light emission of an arbitrary wavelength can be emphasized by adjusting the period of the periodic structure or the film thickness of the photoluminescent layer. For example, if the structure shown in fig. 1A and 1B is made using a photoluminescent material that emits light in a wide frequency band, only light of a certain wavelength can be emphasized. Thus, the light-emitting element 100 shown in fig. 1A and 1B may be made into a powder and used as a fluorescent material. The light-emitting element 100 shown in fig. 1A and 1B may be used by being embedded in resin, glass, or the like.

In the single-body structure shown in fig. 1A and 1B, only a certain specific wavelength can be emitted in a specific direction, and thus it is difficult to realize light emission such as white light having a wide wavelength band spectrum. Therefore, by using a structure in which a plurality of powder-like light-emitting elements 100 having different conditions such as the period of the periodic structure and the film thickness of the photoluminescent layer as shown in fig. 20 are mixed, a light-emitting device having a wide wavelength band spectrum can be realized. In this case, the dimension of each light emitting element 100 in one direction is, for example, about several μm to several mm, and a 1-dimensional or 2-dimensional periodic structure of, for example, several periods to several hundred periods may be included therein.

[ 6-5. arrangement of structures having different periods ]

Fig. 21 is a plan view showing an example in which a plurality of periodic structures having different periods are arranged on a photoluminescent layer in 2-dimension. In this example, 3 kinds of

periodic structures

120a, 120b, 120c are arranged without gaps. The

periodic structures

120a, 120b, and 120c have, for example, periods set so as to emit light in red, green, and blue wavelength ranges to the front surface. By arranging a plurality of structures having different periods on the photoluminescent layer in this manner, directivity can be exhibited also in a wide wavelength band spectrum. The structure of the plurality of periodic structures is not limited to the above structure, and may be set arbitrarily.

[ 6-6. laminated Structure ]

Fig. 22 shows an example of a light-emitting element having a structure in which a plurality of photoluminescent layers 110 each having an uneven structure formed on a surface thereof are stacked. The transparent substrate 140 is provided between the plurality of photoluminescent layers 110, and the uneven structure formed on the surface of each photoluminescent layer 110 corresponds to the periodic structure or the submicron structure. In the example shown in fig. 22, 3 layers of periodic structures having different periods are formed, and the periods are set so that light in red, blue, and green wavelength regions is emitted to the front surface. In addition, the material of the photoluminescent layer 110 of each layer is selected to emit light of a color corresponding to the period of each periodic structure. By stacking a plurality of periodic structures having different periods in this manner, directivity can be exhibited also in a wide wavelength band spectrum.

The number of layers, the photoluminescent layers 110 of each layer, and the structure of the periodic structure are not limited to the above, and may be set arbitrarily. For example, in the 2-layer structure, the 1 st and 2 nd photoluminescent layers are formed correspondingly through the transparent substrate, and the 1 st and 2 nd periodic structures are formed on the surfaces of the 1 st and 2 nd photoluminescent layers, respectively. In this case, the pair of the 1 st photoluminescent layer and the 1 st periodic structure and the pair of the 2 nd photoluminescent layer and the 2 nd periodic structure may satisfy the condition corresponding to the formula (15). In the structure having 3 or more layers, the photoluminescent layer and the periodic structure in each layer may satisfy the condition corresponding to the formula (15). The positional relationship of the photoluminescent layer and the periodic structure may also be reversed from the structure shown in fig. 22. In the example shown in fig. 22, the periods of the respective layers are different, but they may be all the same. In this case, although the spectrum cannot be broadened, the emission intensity can be increased.

[ 6-7. Structure with protective layer ]

Fig. 23 is a cross-sectional view showing an example of a structure in which a protective layer 150 is provided between the photoluminescent layer 110 and the periodic structure 120. Thus, a protective layer 150 for protecting the photoluminescent layer 110 may also be provided. However, when the refractive index of the protective layer 150 is lower than that of the photoluminescent layer 110, the electric field of light is diffused into the protective layer 150 only by about half the wavelength. Thus, when the protective layer 150 is thicker than the wavelength, the light does not reach the periodic structure 120. Therefore, the analog waveguide mode does not exist, and the function of releasing light in a specific direction cannot be obtained. When the refractive index of the protective layer 150 is equal to or greater than the refractive index of the photoluminescent layer 110, light reaches the inside of the protective layer 150. This eliminates the thickness restriction on the protective layer 150. However, in this case, a large part of the portion of the light guide (hereinafter, this portion is referred to as a "waveguide layer") is formed of a photoluminescent material, and a large light output can be obtained. Thus, it is also preferable in this case that the protective layer 150 is thin. The protective layer 150 may be formed using the same material as the periodic structure (light-transmitting layer) 120. In this case, the light-transmitting layer having the periodic structure also serves as a protective layer. The refractive index of the light-transmitting layer 120 is preferably smaller than that of the photoluminescent layer 110.

[7. Material ]

If the photoluminescent layer (or waveguide layer) and the periodic structure are formed of a material satisfying the above conditions, directional light emission can be realized. Any material may be used in the periodic construction. However, if the light absorption of the medium forming the photoluminescent layer (or waveguide layer) or the periodic structure is high, the effect of confining light is reduced, and the peak intensity and Q value are reduced. Thus, as a medium for forming the photoluminescent layer (or waveguide layer) and the periodic structure, a medium having relatively low light absorption can be used.

As the material of the periodic structure, for example, a dielectric having low light absorption can be used. Examples of the material having a periodic structure include MgF₂(magnesium fluoride), LiF (lithium fluoride), CaF₂(calcium fluoride), SiO₂(Quartz), glass, resin, MgO (magnesium oxide), ITO (indium tin oxide), TiO₂(titanium oxide), SiN (silicon nitride), Ta₂O₅(tantalum pentoxide) ZrO₂(zirconia), ZnSe (zinc selenide), ZnS (zinc sulfide), etc.However, when the refractive index of the periodic structure is lower than the refractive index of the photoluminescent layer as described above, MgF having a refractive index of about 1.3 to 1.5 can be used₂、LiF、CaF₂、SiO₂Glass, resin.

The photoluminescent material includes a fluorescent material and a phosphorescent material in a narrow sense, and includes not only an inorganic material but also an organic material (e.g., a pigment) and also quantum dots (i.e., semiconductor fine particles). In general, a fluorescent material having an inorganic material as a matrix tends to have a high refractive index. As a fluorescent material emitting blue light, for example, M can be used₁₀(PO₄)₆Cl₂：Eu²⁺(M is at least 1 selected from Ba, Sr and Ca), BaMgAl₁₀O₁₇：Eu²⁺，M₃MgSi₂O₈：Eu²⁺(M is at least 1 selected from Ba, Sr and Ca), M₅SiO₄Cl₆：Eu²⁺(M is at least 1 selected from Ba, Sr, and Ca). As the fluorescent material emitting green light, for example, M can be used₂MgSi₂O₇：Eu²⁺(M is at least 1 selected from Ba, Sr and Ca), SrSi₅AlO₂N₇：Eu²⁺，SrSi₂O₂N₂：Eu²⁺，BaAl₂O₄：Eu²⁺，BaZrSi₃O₉：Eu²⁺，M₂SiO₄：Eu²⁺(M is at least 1 selected from Ba, Sr and Ca), BaSi₃O₄N₂：Eu²⁺，Ca₈Mg(SiO₄)₄Cl₂：Eu²⁺，Ca₃SiO₄Cl₂：Eu²⁺，CaSi_12－(m+n)Al_(m+n)O_nN_16－n：Ce³⁺，β－SiAlON：Eu²⁺. As the fluorescent material emitting red light, CaAlSiN, for example, can be used₃：Eu²⁺，SrAlSi₄O₇：Eu² ⁺，M₂Si₅N₈：Eu²⁺(M is at least 1 selected from Ba, Sr and Ca), MSiN₂：Eu²⁺(M ═ at least 1 selected from Ba, Sr, and Ca), MSi₂O₂N₂：Yb²⁺(M is at least 1 selected from Sr and Ca), Y₂O₂S：Eu³⁺，Sm³⁺，La₂O₂S：Eu³⁺，Sm³ ⁺，CaWO₄：Li¹⁺，Eu³⁺，Sm³⁺，M₂SiS₄：Eu²⁺(M is at least 1 selected from Ba, Sr and Ca), M₃SiO₅：Eu²⁺(M is at least 1 selected from Ba, Sr, and Ca). As the fluorescent material emitting light in yellow, for example, Y can be used₃Al₅O₁₂：Ce³⁺，CaSi₂O₂N₂：Eu²⁺，Ca₃Sc₂Si₃O₁₂：Ce³⁺，CaSc₂O₄：Ce³⁺，α－SiAlON：Eu²⁺，MSi₂O₂N₂：Eu²⁺(M is at least 1 selected from Ba, Sr and Ca), M₇(SiO₃)₆Cl₂：Eu²⁺(M is at least 1 selected from Ba, Sr, and Ca).

As the quantum dot, for example, a material such as CdS, CdSe, core-shell CdSe/ZnS, or alloy CdSSe/ZnS can be used, and various emission wavelengths can be obtained depending on the material. As the matrix of the quantum dot, for example, glass or resin can be used.

The transparent substrate 140 shown in fig. 1C, 1D, and the like is made of a translucent material having a lower refractive index than the photoluminescent layer 110. Examples of such a material include MgF₂(magnesium fluoride), LiF (lithium fluoride), CaF₂(calcium fluoride), SiO₂(quartz), glass, resin. In a configuration in which the excitation light is incident on the photoluminescent layer 110 without passing through the substrate 140, the substrate 140 does not necessarily have to be transparent.

[8. production method ]

Next, an example of the production method will be described.

As a method for realizing the structure shown in fig. 1C and 1D, for example, there is a method of forming a thin film of the photoluminescent layer 110 on the transparent substrate 140 by a step such as vapor deposition, sputtering, or coating of a fluorescent material, then forming a dielectric, and patterning (patterning) by a method such as photolithography to form the periodic structure 120. Instead of the above method, the periodic structure 120 may be formed by nanoimprinting. As shown in fig. 24, the periodic structure 120 may be formed by processing only a part of the photoluminescent layer 110. In this case, the periodic structure 120 is formed of the same material as the photoluminescent layer 110.

The light-emitting element 100 shown in fig. 1A and 1B can be realized by, for example, performing a step of partially peeling off the photoluminescent layer 110 and the periodic structure 120 from the substrate 140 after the light-emitting element 100a shown in fig. 1C and 1D is manufactured.

The structure shown in fig. 19A can be realized by, for example, forming the periodic structure 120a on the transparent substrate 140 by a method such as a semiconductor process or nanoimprinting, and then forming a material constituting the photoluminescent layer 110 thereon by a method such as vapor deposition or sputtering. Alternatively, the structure shown in fig. 19B may be realized by embedding the photoluminescent layer 110 for the concave portion of the periodic structure 120a by a method such as coating.

The above-described manufacturing method is an example, and the light-emitting element of the present invention is not limited to the above-described manufacturing method.

[9. Experimental example ]

An example of manufacturing a light-emitting element according to an embodiment of the present invention will be described below.

A sample having a light-emitting element with the same structure as that in fig. 19A was produced in a trial manner and characteristics were evaluated. The light-emitting element is manufactured as follows.

A1-dimensional periodic structure (stripe-shaped projections) having a period of 400nm and a height of 40nm was provided on a glass substrate, and a photoluminescent material, YAG: ce forms a film of 210 nm. A TEM image of the cross-sectional view is shown in fig. 25, and a measurement is shown in fig. 26 in which YAG: the spectrum in the front direction when Ce emitted light. Fig. 26 shows the measurement result (ref) in the case where the periodic structure is not present, and the measurement result of the TM mode having a parallel polarization component and the TE mode having a perpendicular polarization component with respect to the 1-dimensional periodic structure. In the case of the periodic structure, light of a specific wavelength can be seen to be significantly increased relative to the case without the periodic structure. Further, it is found that the effect of enhancing light in the TM mode having a polarization component parallel to the 1-dimensional periodic structure is greater.

Fig. 27A to 27F and fig. 28A to 28F show the results of measuring the angle dependence of the intensity of the emitted light on the same sample and the calculation results. Fig. 27A shows a state in which a light emitting element that emits linearly polarized light in the TM mode is rotated about an axis parallel to the row direction of the 1-dimensional periodic structure 120 as a rotation axis. Fig. 27B and 27C show the measurement result and the calculation result for the case of such rotation, respectively. On the other hand, fig. 27D shows a state in which the light emitting element that emits linearly polarized light in the TE mode is rotated about an axis parallel to the row direction of the 1-dimensional periodic structure 120 as a rotation axis. Fig. 27E and 27F show the measurement result and calculation result in this case, respectively. Fig. 28A shows a state in which the light emitting element of linearly polarized light that exits the TE mode is rotated about an axis perpendicular to the row direction of the 1-dimensional periodic structure 120 as a rotation axis. Fig. 28B and 28C show the measurement result and the calculation result in this case, respectively. On the other hand, fig. 28D shows a state in which the light emitting element that emits linearly polarized light in the TM mode is rotated about an axis perpendicular to the row direction of the 1-dimensional periodic structure 120 as a rotation axis. Fig. 28E and 28F show the measurement result and the calculation result in this case, respectively.

As can be seen from fig. 27A to 27F and fig. 28A to 28F, the TM mode is enhanced more effectively. Further, it is known that the wavelength of the light to be intensified shifts with the angle. For example, light having a wavelength of 610nm is in the TM mode and is present only in the front direction, and therefore, it is known that the directivity is high and polarized light emission is performed. Further, since the measurement results of each of fig. 27B and 27C, 27E and 27F, 28B and 28C, and 28E and 28F match the calculation results, the validity of the above calculation is confirmed by an experiment.

Fig. 29 shows the angular dependence of the intensity of light having a wavelength of 610nm when the light is rotated about a rotation axis perpendicular to the row direction as shown in fig. 28D. It can be seen that strong enhancement of light emission occurs in the front direction, and almost all light is not enhanced with respect to angles other than the enhancement. It is understood that the angle of directivity of the light emitted in the front direction is less than 15 °. As described above, the pointing angle is an angle at which the intensity is 50% of the maximum intensity, and is represented by a single angle with the direction of the maximum intensity as the center. From the results shown in fig. 29, it is understood that directional light emission is realized. Further, since the emitted light is all a component of the TM mode, it is known that polarized light emission is also achieved at the same time.

The above experiment for verification used YAG that emits light at a wavelength band of a broad band: ce. Even when an experiment is performed using a photoluminescent material that emits light in a narrow band with the same structure, high directivity and polarized light emission can be achieved for light of the wavelength. Further, when such a photoluminescent material is used, since light of other wavelengths is not generated, a light source that does not generate light in other directions or in other polarization states can be realized.

[10. other modifications ]

Next, another modified example of the light-emitting element and the light-emitting device of the present invention will be described.

As described above, with the submicron structure included in the light-emitting element of the present invention, the wavelength and the emission direction of light having an emission enhancement effect depend on the structure of the submicron structure. A light-emitting element having the periodic structure 120 on the photoluminescent layer 110 shown in fig. 31 can be considered. Here, the case where the periodic structure 120 is formed of the same material as the photoluminescent layer 110 and has the 1-dimensional periodic structure 120 shown in fig. 1A is exemplified. Light subjected to luminescence enhancement by the 1-dimensional periodic structure 120 has a refractive index n of the photoluminescent layer 110, given the period p (nm) of the 1-dimensional periodic structure 120_wavRefractive index n of external medium from which light is emitted_outThe incident angle to the 1-dimensional periodic structure 120 is θ_wavAnd the emission angle from the 1-dimensional periodic structure 120 to the medium outside is θ_outThen, p × n is satisfied_wav×sinθ_wav－p×n_out×sinθ_outThe relationship is m λ (see the above equation (5)). Where λ is the wavelength of light in air and m isAn integer number.

From the above equation, θ can be obtained_out＝arcsin[(n_wav×sinθ_wav－mλ/p)/n_out]. Thus, in general, if the wavelengths λ are different, the exit angle θ of the light subjected to luminescence enhancement_outDifferent. As a result, as schematically shown in fig. 31, the visible color differs depending on the direction of observation.

To reduce this viewing angle dependency, n is selected_wavAnd n_outSo that (n)_wav×sinθ_wav－mλ/p)/n_outIt is not necessarily required depending on the wavelength λ. Since the refractive index of a substance has wavelength dispersion (wavelength dependence), it is only necessary to select a substance having (n)_wav×sinθ_wav－mλ/p)/n_outIndependent of n as wavelength lambda_wavAnd n_outThe wavelength dispersive material of (1) may be used. For example, in the case where the external medium is air, n_outSince the refractive index is approximately 1.0 regardless of the wavelength, it is preferable to select the refractive index n as the material for forming the photoluminescent layer 110 and the 1-dimensional periodic structure 120_wavA less dispersed material. Further, it is preferable for the refractive index n_wavA reverse dispersion material in which the refractive index of light with a shorter wavelength is low.

Further, as shown in fig. 32A, white light can be emitted by arranging a plurality of periodic structures having different wavelengths that exhibit a mutual light emission enhancement effect. In the example shown in fig. 32A, a periodic structure 120R capable of enhancing red light (R), a periodic structure 120G capable of enhancing green light (G), and a periodic structure 120B capable of enhancing blue light (B) are arranged in a matrix. The

periodic structures

120r, 120g, and 120b are, for example, 1-dimensional periodic structures, and respective convex portions are arranged in parallel with each other. Thus, the polarization characteristics are the same for all colors of red, green, and blue. By the

periodic structures

120r, 120g, and 120b, light of three primary colors subjected to emission enhancement is emitted, and as a result of color mixing, white light and linearly polarized light can be obtained.

If the

periodic structures

120r, 120g, and 120b arranged in a matrix are referred to as unit periodic structures (or pixels), the size of the unit periodic structure (i.e., the length of one side) is, for example, 3 times or more the period. In order to obtain the effect of color mixing, the unit period structure is preferably not recognized by human eyes, and the length of one side is preferably smaller than 1mm, for example. Here, each unit periodic structure is depicted as a square, but the present invention is not limited to this, and for example, the

periodic structures

120r, 120g, and 120b adjacent to each other may have a shape other than a square, such as a rectangle, a triangle, or a hexagon.

Note that the photoluminescent layers provided below the

periodic structures

120r, 120g, and 120b may be common to the

periodic structures

120r, 120g, and 120b, or may be provided with photoluminescent layers containing different photoluminescent materials corresponding to the respective colors of light.

As shown in fig. 32B, a plurality of periodic structures (including

periodic structures

120h, 120i, and 120j) having different orientations in which the projections of the 1-dimensional periodic structure extend may be arranged. The wavelengths of the light with enhanced luminescence of the plurality of periodic structures may be the same or different. For example, if the same periodic structure is arranged as shown in fig. 32B, unpolarized light can be obtained. Further, if the arrangement of fig. 32B is applied to each of the

periodic structures

120r, 120g, and 120B in fig. 32A, white light of unpolarized light can be obtained as a whole.

Of course, the periodic structure is not limited to the 1-dimensional periodic structure, and a plurality of 2-dimensional periodic structures (including the

periodic structures

120k, 120m, and 120n) may be arranged as shown in fig. 32C. In this case, the periods and orientations of the

periodic structures

120k, 120m, and 120n may be the same or different as described above, and may be appropriately set as needed.

As shown in fig. 33, for example, an array of microlenses 130 may be disposed on the light-emitting side of the light-emitting element. By bending the light emitted obliquely in the normal direction by the array of microlenses 130, the effect of color mixing can be obtained.

The light emitting element shown in fig. 33 has regions R1, R2, and R3 having the

periodic structures

120R, 120g, and 120b in fig. 32A, respectively. In the region R1, the periodic structure 120R causes the red light R to be emitted in the normal direction, and causes the green light G to be emitted in the oblique direction, for example. The green light G emitted obliquely is bent in the normal direction by the refraction action of the microlens 130. As a result, in the normal direction, red light R and green light G are observed by color mixing. By providing the microlens 130 in this manner, it is possible to suppress a phenomenon in which the wavelength of the emitted light differs depending on the angle. Here, a microlens array in which a plurality of microlenses corresponding to a plurality of periodic structures are integrated is illustrated, but the present invention is not limited thereto. Of course, the periodic structure of the tiling (tiling) is not limited to the above example, and can be applied to the case where the same periodic structure is tiled, and can also be applied to the structure shown in fig. 32B or 32C.

Instead of the microlens array, a lenticular lens (lens) may be used as the optical element having the function of bending the obliquely emitted light. In addition, not only the lens but also a prism may be used. An array of prisms may also be used. The prisms may be arranged respectively corresponding to the periodic structure. The shape of the prism is not particularly limited. For example, a triangular prism or a pyramid type prism may be used.

In addition to the method based on the periodic structure, a method based on a photoluminescent layer may be used to obtain white light (or light having a wide spectral width), for example, as shown in fig. 34A and 34B. As shown in fig. 34A, white light can be obtained by laminating a plurality of

photoluminescent layers

110b, 110g, and 110r having different emission wavelengths. The stacking order is not limited to the illustrated example. As shown in fig. 34B, a photoluminescent layer 110y that emits yellow light may be stacked on a photoluminescent layer 110B that emits blue light. The photoluminescent layer 110y can be formed using YAG, for example.

In addition, when a photoluminescent material in which a fluorescent dye or the like is mixed with a host (host) material is used, a plurality of photoluminescent materials having different emission wavelengths can be mixed with the host material, and white light can be emitted by a single photoluminescent layer. The photoluminescent layer capable of emitting white light can be used in the structure in which the unit period structure is applied as described with reference to fig. 32A to 32C.

In the case where an inorganic material (for example, YAG) is used as a material for forming the photoluminescent layer 110, heat treatment at a temperature exceeding 1000 ℃ may be performed during the production thereof. At this time, impurities may diffuse from the base (typically, substrate) to degrade the light emission characteristics of the photoluminescent layer 110. In order to prevent diffusion of impurities into the photoluminescent layer, for example, as shown in fig. 35A to 35D, a diffusion preventing layer (barrier layer) 108 may be provided below the photoluminescent layer. As shown in fig. 35A to 35D, the diffusion preventing layer 108 is formed below the photoluminescent layer 110 in the various structures exemplified so far.

For example, as shown in fig. 35A, the diffusion preventing layer 108 is formed between the substrate 140 and the photoluminescent layer 110. In addition, as shown in fig. 35B, when a plurality of photoluminescent layers 110a and 110B are provided, a diffusion preventing layer 108a or 108B is formed below each of the photoluminescent layers 110a and 110B.

In the case where the refractive index of the substrate 140 is larger than that of the photoluminescent layer 110, it is advantageous if the low refractive index layer 107 is formed on the substrate 140 as shown in fig. 35C and 35D. As shown in fig. 35C, in the case where the low refractive index layer 107 is provided on the substrate 140, the diffusion preventing layer 108 is formed between the low refractive index layer 107 and the photoluminescent layer 110. Further, as shown in fig. 35D, when a plurality of

photoluminescent layers

110a and 110b are provided,

diffusion preventing layers

108a and 108b are formed below the

photoluminescent layers

110a and 110b, respectively.

The low refractive index layer 107 may be formed when the refractive index of the substrate 140 is equal to or greater than the refractive index of the photoluminescent layer 110. The refractive index of the low refractive index layer 107 is lower than that of the photoluminescent layer 110. Low refractive index layer 107, for example, MgF is used₂、LiF、CaF₂、BaF₂、SrF₂And room temperature hardening glass such as quartz, resin, HSQ and SOG. The thickness of the low refractive index layer 107 is preferably larger than the wavelength of light. MgF is used for the substrate 140, for example₂、LiF、CaF₂、BaF₂、SrF₂Glass (e.g. soda lime glass), resin, MgO, MgAl₂O₄Sapphire (Al)₂O₃)、SrTiO₃、LaAlO₃、TiO₂、Gd₃Ga₅O₁₂、LaSrAlO₄、LaSrGaO₄、LaTaO₃、SrO、YSZ(ZrO₂·Y₂O₃)、YAG、Tb₃Ga₅O₁₂And (4) forming.

The

diffusion preventing layers

108, 108a, and 108b may be appropriately selected depending on the element to be prevented from being diffused, and may be formed using, for example, an oxide crystal or a nitride crystal having a strong covalent bond bonding property. The thicknesses of the

diffusion preventing layers

108, 108a, and 108b are, for example, 50nm or less.

In a structure including a layer adjacent to the photoluminescent layer 110, such as the diffusion barrier layer 108 or the crystal growth layer 106 described later, when the refractive index of the adjacent layer is larger than the refractive index of the photoluminescent layer, the refractive index of the layer having a larger refractive index and the refractive index of the photoluminescent layer are weighted by the volume ratio of each of the refractive index and the refractive index, and the average refractive index is defined as n_wav. This is because, in this case, it is optically equivalent to the case where the photoluminescent layer is composed of a plurality of layers of different materials.

In the photoluminescent layer 110 formed using an inorganic material, the crystallinity of the inorganic material is low, and therefore, the luminescent characteristics of the photoluminescent layer 110 may be low. In order to improve the crystallinity of the inorganic material constituting the photoluminescent layer 110, as shown in fig. 36A, a crystal growth layer (also referred to as a "seed layer") 106 may be formed on the substrate of the photoluminescent layer 110. The crystal growth layer 106 is formed using a material lattice-matched to the crystal of the photoluminescent layer 110 formed thereon. The lattice match is preferably within, for example, ± 5%. In the case where the refractive index of the substrate 140 is greater than that of the photoluminescent layer 110, it is advantageous if the refractive index of the

crystal growth layer

106 or 106a is smaller than that of the photoluminescent layer 110.

When the refractive index of the substrate 140 is larger than that of the photoluminescent layer 110, as shown in fig. 36B, the low refractive index layer 107 may be formed on the substrate 140. Since the crystal growth layer 106 is in contact with the photoluminescent layer 110, when the low refractive index layer 107 is formed on the substrate 140, the crystal growth layer 106 is formed on the low refractive index layer 107. In addition, as shown in fig. 36C, in the structure including the plurality of

photoluminescent layers

110a and 110b, it is advantageous to form the

crystal growth layers

106a and 106b corresponding to the plurality of

photoluminescent layers

110a and 110b, respectively. The thickness of each of the crystal growth layers 106, 106a, and 106b is, for example, 50nm or less.

As shown in fig. 37A and 37B, a surface protective layer 132 may be provided to protect the periodic structure 120. In the example shown in fig. 37A and 37B, the surface protective layer 132 covers the periodic structure 120, and the surface of the photoluminescent layer 110 of the surface protective layer 132 is flat.

The surface protection layer 132 may be of a type having no substrate as shown in fig. 37A, or may be of a type having a substrate 140 as shown in fig. 37B. In the light-emitting element of the type without a substrate shown in fig. 37A, a surface protective layer may be provided also below the photoluminescent layer 110. In this way, the surface protective layer 132 may be provided on the surface of any of the light-emitting elements described above. The periodic structure 120 is not limited to the structures illustrated in fig. 37A and 37B, and may be any of the types described above. For example, the periodic structure 120 may be a structure formed of the same material as the photoluminescent layer 110 (refer to fig. 24). In this case, the air layer can also be said to be a light-transmitting layer.

The surface protection layer 132 may be made of, for example, resin, hard coat (hard coat) material, or SiO₂、Al₂O₃(alumina), SiOC, DLC. The thickness of the surface protective layer 132 is, for example, 100nm to 10 μm.

By providing the surface protective layer 132, the light-emitting element can be protected from the external environment, and deterioration of the light-emitting element can be suppressed. The surface protective layer 132 protects the surface of the light emitting element from scratches, moisture, oxygen, acid, alkali, or heat. The material and thickness of the surface protection layer 132 may be appropriately set according to the purpose.

In addition, the material of the substrate 140 may be deteriorated by heat. Heat is generated primarily by non-radiative losses or stokes losses of the photoluminescent layer 110. For example, the thermal conductivity of quartz (1.6W/mK) is about 1 bit smaller than that of YAG (11.4W/mK). Therefore, heat generated in the photoluminescent layer (for example, YAG layer) 110 is not easily conducted to the outside through the substrate (for example, quartz substrate) 140 and is thus dissipated, and the temperature of the photoluminescent layer 110 may increase to cause thermal degradation.

Therefore, as shown in fig. 38A, by forming the transparent high thermal conductive layer 105 between the photoluminescent layer 110 and the substrate 140, the heat of the photoluminescent layer 110 can be efficiently conducted to the outside, and the temperature rise can be prevented. At this time, the refractive index of the transparent high heat conductive layer 105 is preferably lower than that of the photoluminescent layer 110. In addition, when the refractive index of the substrate 140 is lower than the refractive index of the photoluminescent layer 110, the refractive index of the transparent high thermal conductive layer 105 may be higher than the refractive index of the photoluminescent layer 110. However, in this case, since the transparent high thermal conductive layer 105 forms a wave guide layer together with the photoluminescent layer 110, it is advantageous if it is 50nm or less. When soda lime glass, for example, is used as the material of the substrate 140, the material for forming the transparent high thermal conductive layer 105 may be determined in consideration of the refractive index of the substrate 140. As shown in fig. 38B, if the low refractive index layer 107 is formed between the photoluminescent layer 110 and the transparent high heat conductive layer 105, a thicker transparent high heat conductive layer 105 can be utilized.

Further, as shown in fig. 38C, the periodic structure 120 may be covered with a low refractive index layer 107 having a high thermal conductivity. Further, as shown in fig. 38D, the transparent high thermal conductive layer 105 may be formed after the periodic structure 120 is covered with the low refractive index layer 107. In this structure, the low refractive index layer 107 does not need to have high thermal conductivity.

As a material of the transparent high thermal conductive layer 105, for example, Al can be cited₂O₃、MgO、Si₃N₄、ZnO、AlN、Y₂O₃Diamond, graphite, CaF₂、BaF₂. Among them, CaF₂、BaF₂Since the refractive index is low, it can be used as the low refractive index layer 107.

[11 ] other embodiments of the light-emitting element ]

[ 11-1. improvement of quantity of light emitted to the outside ]

According to the configuration described above, narrow-angle light distribution that is not dependent on optical members such as reflectors and lenses can be achieved. According to at least one of the above aspects, for example, the directivity angle of the light emitted in the front direction can be reduced to about 15 ° with respect to a specific wavelength, and the various aspects described above are particularly useful for optical devices that are required to have a relatively small directivity angle. On the other hand, there are also applications in which high directivity is not required, such as general lighting equipment, headlights and tail lights of vehicles, and the like. In such applications, it is beneficial if more light is output from the light emitting element.

The directivity of the light-emitting element of the present invention with respect to a specific wavelength is presumably realized by forming an analog guided wave mode inside the photoluminescent layer and extracting light in the analog guided wave mode to the outside of the light-emitting element based on the interaction between the analog guided wave mode and the periodic structure. Therefore, if the light emitting element is made to emit the light in the analog guided wave mode to the outside, it is expected that the amount of light emitted from the light emitting element to the outside can be increased.

As described with reference to fig. 8 to 11, the ratio of the light emitting element to emit the light in the pseudo-guided mode to the outside varies depending on the refractive index of the material constituting the periodic structure and the height of the periodic structure. As described with reference to fig. 8 and 9, if the refractive index of the periodic structure is increased, the effect of light confinement is reduced (it can be said that the Q value is decreased). Therefore, if the refractive index of the periodic structure is increased, it is expected that more light can be extracted to the outside of the light emitting element. In addition, similarly, when the height of the periodic structure is increased, the ratio of the light emitting element to emit light in the analog waveguide mode to the outside can be increased. In this case, it is advantageous if the proportion of high-order light in the light emitted to the outside of the light-emitting element can be reduced.

[ 11-2. relationship between the cross-sectional shape of the surface shape and the directivity ]

The present inventors have found that when the cross-sectional shape of the periodic structure is expressed by using a fourier series, the proportion of high-order light emitted from the light emitting element can be estimated from what high-order terms are included in the series. According to the results of the studies by the present inventors, when looking at a certain wavelength, the frequency of light emitted from the light emitting element is correlated with the frequency of the frequency component contained in the fourier series expansion of the cross-sectional shape of the periodic structure. That is, if the fourier series expansion of the cross-sectional shape of the periodic structure contains a high-order frequency component, light of a high order corresponding to the number of terms of the fourier series is emitted from the light emitting element.

Fig. 39 is a graph showing the result of calculating a trigonometric series including terms only 1 time (sine wave), within 3 times, within 5 times, and within 11 times. In fig. 39, a graph showing a rectangular wave is also shown together. As illustrated, the shape of the graph of the triangular order approaches a rectangular wave as the high frequency component increases. Therefore, as shown in fig. 40, a large amount of high-order light having different numbers of times is emitted from a light-emitting element having a periodic structure including a plurality of convex portions (or concave portions) having a rectangular cross-sectional shape. That is, the ratio of light of 1 st order among light emitted from such a light-emitting element can be said to be relatively low.

From the viewpoint of increasing the proportion of light of order 1, it is advantageous that the fourier series expansion of the cross-sectional shape of the periodic structure does not contain a higher-order term. From the viewpoint of increasing the proportion of light of order 1, a periodic structure (fig. 41A) including a plurality of convex portions having a triangular cross-sectional shape, which includes fewer high-order terms in the fourier series expansion, is advantageous compared to a periodic structure (fig. 40) including a plurality of convex portions having a rectangular cross-sectional shape. Since the sine wave is composed of only frequency components of order 1 (see fig. 39), the proportion of light emitted in the order 1 in a specific direction can be increased as the cross-sectional shape of the periodic structure is closer to the sine wave (fig. 41B).

[ 11-3. light-emitting element ]

Fig. 42 schematically shows an exemplary cross section of a light-emitting element according to another embodiment of the present invention. The light-emitting element 100b shown in fig. 42 includes a substrate 140 and a photoluminescent layer 110 supported on the substrate 140. In the structure illustrated in fig. 42, the periodic structure 120b is formed on the surface of the photoluminescent layer 110 opposite to the substrate 140. In this example, similarly to the structure described with reference to fig. 19A, the periodic structure 120a is formed on the surface of the substrate 140 on the side of the photoluminescent layer 110. The

periodic structures

120a and 120b limit the pointing angle of light having a specific wavelength among the light emitted from the photo-luminescent layer 110.

In the example described here, the substrate 140 is substantially planar. The main surface PS of the substrate 140 on the side opposite to the photoluminescent layer 110 is typically a flat surface, where the main surface PS is parallel to the xy-plane. The substrate 140 and the photoluminescent layer 110 are stacked along the z-direction. Fig. 42 schematically shows a cross section (i.e., a vertical cross section) of the light-emitting element 100b perpendicular to the photoluminescent layer 110 and parallel to the arrangement direction of the plurality of projections in the periodic structure 120 b.

The periodic structure 120b on the photoluminescent layer 110 includes a plurality of convex portions. The plurality of projections in the periodic structure 120b includes at least 1 projection having a base portion with a width larger than a top portion when viewed from a vertical cross section. The periodic structure 120b may partially include 1 or more convex portions having a cross-sectional shape in which the base portion has a larger width than the top portion. Alternatively, each of the plurality of projections may have a base portion having a width larger than that of the top portion.

In the illustrated example, the cross-sectional shape of each of the 4 projections arranged along the x-direction is a trapezoidal shape, and for example, if attention is paid to the projection 122b located at the rightmost side in the figure, the width Bs of the base portion of the projection 122b is larger than the width Tp of the top portion.

By making the periodic structure 120b include at least 1 convex portion having a base portion larger in width than a top portion when a vertical cross section is viewed, an abrupt change in height along the arrangement direction in the cross-sectional shape of the periodic structure 120b can be suppressed. Therefore, by making the periodic structure 120b include at least 1 convex portion having a base portion whose width is larger than that of the top portion when the vertical cross section is viewed, the cross-sectional shape of the periodic structure can be made close to a sine wave, and the proportion of 1-time light emitted toward a specific direction can be increased.

As illustrated, the convex portion 122b may have a side surface inclined with respect to a direction perpendicular to the photoluminescent layer 110 (here, parallel to the z direction). In other words, the periodic structure 120b may also include at least 1 convex portion whose sectional area increases as the plane (here, xy plane) parallel to the photoluminescent layer 110 approaches the substrate 140 when cut off. In this example, the sectional area of the convex portion 122b in the plane parallel to the photoluminescent layer 110 is largest at the portion closest to the photoluminescent layer 110. The sectional area of the convex portion in a plane parallel to the photoluminescent layer 110 may increase monotonously from the top toward the base, or may increase in a portion between the top and the base.

In the case where the periodic structure 120b includes a plurality of concave portions, the plurality of concave portions may include at least 1 concave portion having an opening portion whose width is larger than that of the bottom portion when the vertical cross section is viewed. The periodic structure 120b may partially include 1 or more recessed portions having such a cross-sectional shape, or a plurality of recessed portions may have opening portions each having a width larger than that of the bottom portion. In the structure illustrated in fig. 42, in the case where it is explained that the periodic structure 120b includes the concave portion 124b, it can be said that the side surface of the concave portion 124b is inclined with respect to the direction perpendicular to the photoluminescent layer 110. Alternatively, when the periodic structure 120b is cut by a plane parallel to the photoluminescent layer 110, the opening area of the recess 124b may be reduced as the plane approaches the substrate 140. In this example, the opening area of the concave portion 124b in a plane parallel to the photoluminescent layer 110 is smallest at a portion closest to the substrate 140. By making the periodic structure 120b include at least 1 concave portion having an opening portion larger in width than the bottom portion when the vertical cross section is viewed, the same effect can be obtained as in the case where the periodic structure 120b includes at least 1 convex portion having a base portion larger in width than the top portion when the vertical cross section is viewed. The periodic structure 120b may be formed using the same material as the photoluminescent layer 110 or may be formed using a different material from the photoluminescent layer 110.

As described above, the periodic structure 120a is formed on the substrate 140. The periodic structure 120a includes a plurality of projections. The periodic structure 120a may be formed using the same material as the substrate 140 or may be formed using a material different from the substrate 140. The photoluminescent layer 110 is formed on the substrate 140 so as to cover the plurality of projections. In the structure illustrated in fig. 42, the plurality of convex portions in the periodic structure 120b on the photoluminescent layer 110 are respectively located on each of the plurality of convex portions in the periodic structure 120a on the substrate 140.

In the structure illustrated in fig. 42, the substrate 140 is typically a transparent substrate and can function as a light-transmitting layer disposed close to the photoluminescent layer 110. In this example, the substrate 140 as a light-transmitting layer is in contact with the photoluminescent layer 110, and the periodic structure 120a is formed at the boundary between the light-transmitting layer and the photoluminescent layer 110 as it is. In the illustrated example, since the periodic structure 120b is formed on the photoluminescent layer 110, the light-emitting element 100b may further include another light-transmitting layer on the side opposite to the substrate 140 of the photoluminescent layer 110.

As described with reference to fig. 35A to 35D, fig. 36A to 36C, fig. 38A, and fig. 38B, intermediate layers such as the diffusion preventing layer 108, the low refractive index layer 107, the crystal growth layer 106, and the transparent high thermal conductive layer 105 may be disposed between the photoluminescent layer 110 and the substrate 140. At this time, the periodic structure 120a is disposed at the boundary between the transparent layer and the photoluminescent layer 110. When the refractive index of the intermediate layer is larger than the refractive index of the photoluminescent layer, the average refractive index obtained by weighting the refractive index of the intermediate layer and the refractive index of the photoluminescent layer by the volume ratio of each of the refractive indices is n_wavIt is sufficient. When the refractive index of the intermediate layer is smaller than the refractive index of the photoluminescent layer, the intermediate layer hardly affects the guided wave mode, and therefore, it is not necessary to consider the refractive index of the intermediate layer.

In fig. 42, the thick solid line arrows schematically indicate light extracted to the outside of the light-emitting element 100b by interaction with the periodic structure 120a on the substrate 140, and the thick dashed line arrows schematically indicate light extracted to the outside of the light-emitting element 100b by interaction with the periodic structure 120b on the photoluminescent layer 110. In the embodiment described here, the

periodic structures

120a and 120b are provided on the surface of the light-transmitting layer (here, the substrate 140) on the side of the photoluminescent layer 110 and on the surface of the photoluminescent layer 110 on the side opposite to the light-transmitting layer, respectively. According to such a configuration, as schematically shown in fig. 42, light whose traveling direction is changed to a specific direction by the interaction with the periodic structure 120a and light whose traveling direction is changed to a specific direction by the interaction with the periodic structure 120b are extracted to the outside of the light emitting element 100 b. In other words, the same effect as that obtained when the height or refractive index of the periodic structure 120a or the height or refractive index of the periodic structure 120b is increased can be obtained in practice. By providing periodic structures on the surface of the light-transmitting layer on the side of the photoluminescent layer 110 and on the surface of the photoluminescent layer 110 on the side opposite to the light-transmitting layer, the amount of light extracted to the outside of the light-emitting element 100b can be increased as a whole. Therefore, the application range of the light-emitting element can be further expanded.

In addition, the period p1 of the periodic structure 120a (here, equal to the center-to-center distance between two adjacent convex portions) and the period p2 of the periodic structure 120b (here, equal to the center-to-center distance between two adjacent convex portions) may be the same or different. If p1 is equal to p2, the emission intensity of a specific wavelength can be increased, and if p1 is different from p2, the spectrum can be broadened. The periods p1 and p2 may be determined based on the above equation (15).

By providing the

periodic structures

120a and 120b on the surface of the substrate 140 and the surface of the photoluminescent layer 110, which are light-transmitting layers, respectively, a synergistic effect with the cross-sectional shape of the periodic structure 120b on the photoluminescent layer 110 can be obtained. As a result, a higher effect of enhancing the light emission can be obtained with respect to the light of a specific wavelength emitted in a specific direction. Of course, a combination of methods for increasing the height or refractive index of the periodic structure 120a and/or the height or refractive index of the periodic structure 120b may be used.

In addition, as for the plurality of projections or recesses constituting the periodic structure, the "inclination angle" of the side surface may be defined. Fig. 43 schematically shows a part of a vertical cross section of a periodic structure including a plurality of projections Pt. Regarding each side surface Ls of the convex portion Pt included in the range of interest among the plurality of convex portions Pt included in the periodic structure, the magnitude of an angle θ (0 ° ≦ θ ≦ 90 °) formed by an axis N1 indicating a direction perpendicular to the photoluminescent layer 110 and a normal Np of the side surface Ls is obtained, and the arithmetic average of these values is defined as "inclination angle" of the side surface. Where θ is the angle measured from axis N1 toward normal Np. For example, when the side surface Ls includes a plurality of surfaces, such as a step-like cross-sectional shape, the angle θ may be obtained for each surface and the average value of the angles may be used. The angle θ can be measured by fitting (fitting) an image obtained by imaging a cross section of the light emitting element, for example.

In the case where the profile of the vertical cross section of the side surface Ls includes a curved portion, as for the curved portion thereof, it is sufficient to adopt an average value of the above-described angle θ from the starting point to the end point of the curved portion thereof. In the case where the periodic structure is formed by a plurality of concave portions, the "inclination angle" can be defined similarly to the case where the periodic structure is formed by a plurality of convex portions.

In the structure illustrated in fig. 43, the cross-sectional shape of each of the 4 convex portions arranged in the x direction on the photoluminescent layer 110 is a trapezoidal shape, and the cross-sectional shape of each of the 4 convex portions arranged in the x direction on the substrate 140 is a rectangular shape. In this example, the inclination angle of the side surfaces of the plurality of convex portions in the periodic structure 120b on the photoluminescent layer 110 is smaller than the inclination angle (here, 90 °) of the side surfaces of the plurality of convex portions in the periodic structure 120a on the substrate 140. When the periodic structure 120b and the periodic structure 120a are each formed of a plurality of concave portions, the inclination angles of the side surfaces of the plurality of concave portions in the periodic structure 120b may be smaller than the inclination angles of the side surfaces of the plurality of concave portions in the periodic structure 120 a.

[ 11-4. relationship between the inclination angle of the side face and the degree of enhancement of light ]

The inventors of the present invention performed optical analysis using diffactmod manufactured by サイバネット, and examined the influence of the cross-sectional shape of the periodic structure on the degree of light enhancement. Here, similarly to the calculation described with reference to fig. 2 and the like, the degree of enhancement of light emitted perpendicularly to the outside is obtained by calculating an increase or decrease in absorption of light in the photoluminescent layer when light is incident perpendicularly to the light-emitting element from the outside. As a model for calculation, a cross-sectional shape as shown in fig. 43 is assumed.

In the following calculation, it is assumed that the respective sectional shapes (here, trapezoidal shapes) of the plurality of convex portions in the periodic structure 120b on the photoluminescent layer 110 are common therebetween. Further, it is assumed that the respective sectional shapes (rectangular shapes here) of the plurality of projections in the periodic structure 120a on the substrate 140 are also common therebetween. That is, here, a 1-dimensional periodic structure uniform in the y direction is assumed as a model of calculation.

In the following calculation, the refractive index of the substrate 140 is 1.5, and the refractive index of the photoluminescent layer 110 is 1.8. In the calculation, it is assumed that the material constituting the periodic structure 120b is common to the material constituting the photoluminescent layer 110, and that the material constituting the periodic structure 120a is common to the material constituting the substrate 140. The distance h3 from the base of the convex portion of the periodic structure 120a to the base of the convex portion of the periodic structure 120b was 240nm, and the height h1 of the convex portion of the periodic structure 120a and the height h2 of the convex portion of the periodic structure 120b were 100 nm. The period p1 of the periodic structure 120a and the period p2 of the periodic structure 120b are both 400 nm.

Fig. 44 shows the result of calculating the degree of enhancement of light emitted in the front direction by changing the inclination angle of the side surfaces of the plurality of projections in the periodic structure 120 b. Further, the area of the top and the base is adjusted so that the area of the vertical cross section of the convex portion becomes constant when the inclination angle of the side surface of the convex portion is changed, assuming that the polarized light of the light is calculated by the TM mode having an electric field component parallel to the y direction.

As is clear from fig. 44, the effect of enhancing light emission at a specific wavelength can be improved by reducing the inclination angle of the side surfaces of the plurality of projections arranged on the photoluminescent layer 110 to about 40 °. This is considered because the cross-sectional shape of the periodic structure is close to a sine wave, and the proportion of light emitted 1 time in a specific direction increases. As described above, for example, by making the inclination angle of the side surface of the plurality of convex portions in the periodic structure 120b smaller than the inclination angle of the side surface of the plurality of convex portions in the periodic structure 120a, a higher effect of enhancing light emission with respect to a specific wavelength can be expected.

[ 11-5 ] modifications of light-emitting elements ]

Fig. 45 shows another example of a light-emitting element in which a periodic structure including projections having inclined side surfaces is formed on a photoluminescent layer 110. A light-emitting element 100c shown in fig. 45 is different from the light-emitting element 100b shown in fig. 43 in that, in the light-emitting element 100c, the periodic structure 120a formed on the substrate 140 includes a plurality of convex portions having inclined side surfaces.

In the structure illustrated in fig. 45, in the periodic structure 120a, each cross-sectional shape of 4 projections arranged along the x direction is a trapezoidal shape. For example, if attention is paid to the convex portion 122a on the rightmost side in the figure, the width Bs of the base portion of the convex portion 122a is larger than the width Tp of the top portion, as with the corresponding convex portion 122 b. In this way, the periodic structure 120a on the substrate 140 may include 1 or more projections having a base portion with a width larger than that of the top portion. In this example, the side surface of the convex portion 122a is inclined with respect to the direction perpendicular to the photoluminescent layer 110.

In this example, the periodic structure 120a on the substrate 140 may be interpreted to include a plurality of concave portions. In this case, for example, the concave portion 124a in the periodic structure 120a has an opening portion having a width larger than the bottom portion when the vertical cross section is viewed. The periodic structure 120a may include 1 or more concave portions having such a cross-sectional shape. The side surfaces of the concave portions 124a are inclined with respect to the direction perpendicular to the photoluminescent layer 110, and when the periodic structure 120a is cut by a plane parallel to the photoluminescent layer 110, the opening area of the concave portions 124a decreases as the plane is separated from the periodic structure 120 b. In this example, the opening area of the concave portion 124a in a plane parallel to the photoluminescent layer 110 is smallest at a portion closest to the substrate 140.

Fig. 46 shows the results of calculating the degree of enhancement of light emitted in the front direction by changing the inclination angles of the side surfaces of the plurality of projections in the periodic structure 120b on the photoluminescent layer 110 and the periodic structure 120a on the substrate 140. Here, assuming that the cross-sectional shape of each of the plurality of projections in the periodic structure 120b on the photoluminescent layer 110 is common to the cross-sectional shape of each of the plurality of projections in the periodic structure 120a on the substrate 140 (here, a trapezoidal shape), the same calculation as the optical analysis described with reference to fig. 44 is performed. As is clear from fig. 46, the effect of enhancing the light emission with respect to a specific wavelength can be improved by reducing the inclination angle of the side surfaces of the plurality of projections to about 40 °.

Fig. 47 shows the calculation results when the cross-sectional shapes of the plurality of projections in the periodic structure 120b on the photoluminescent layer 110 are rectangular and the cross-sectional shapes of the plurality of projections in the periodic structure 120a on the substrate 140 are trapezoidal. As shown in fig. 47, if the side surfaces of the plurality of projections in the periodic structure 120a on the substrate 140 are inclined with respect to the direction perpendicular to the photoluminescent layer 110, the degree of enhancement with respect to light of a specific wavelength tends to increase as the inclination angle becomes smaller.

[ 11-6. other exemplary sectional shapes of periodic Structure ]

The cross-sectional shape of each of the plurality of projections in the periodic structure 120a and the periodic structure 120b is not limited to a rectangular shape or a trapezoidal shape, and may be various shapes.

Fig. 48A to 48D show another example of the cross-sectional shape of the periodic structure. The periodic structure 120d shown in fig. 48A, the periodic structure 120e shown in fig. 48B, and the periodic structure 120f shown in fig. 48C include a plurality of projections 122d, a plurality of projections 122e, and a plurality of projections 122f, respectively. Fig. 48A shows a structure in which a portion of the side surface of the convex portion 122d closer to the base of the convex portion 122d is curved. Fig. 48B shows a structure in which a portion of the side surface of the convex portion 122e closer to the top of the convex portion 122e is curved. Fig. 48C shows a structure in which a portion of the side surface of the convex portion 122f closer to the top of the convex portion 122f is curved. In this way, the profile of the vertical cross section of the convex portion (or concave portion) constituting the periodic structure may include a curved portion. If at least a part of the side surfaces of the plurality of projections (or recesses) in the periodic structure 120b on the photoluminescent layer 110 and/or at least a part of the side surfaces of the plurality of projections (or recesses) in the periodic structure 120a on the substrate 140 are inclined with respect to the direction perpendicular to the photoluminescent layer 110, the proportion of light of a high order of light of a specific wavelength emitted in a specific direction can be reduced. In the example shown in the figure, the width Bs of the base portion of each of the

convex portions

122d, 122e, and 122f is larger than the width Tp of the top portion.

The periodic structure 120g shown in fig. 48D has a profile of a side surface of a vertical section including a plurality of projections 122g stepped. In this way, the side surfaces of the convex portions (or concave portions) constituting the periodic structure 120a and/or the side surfaces of the convex portions (or concave portions) constituting the periodic structure 120b may include a stepped portion in a part thereof. In this example, the shape of the right side surface of the convex portion is symmetrical to the shape of the left side surface of the convex portion, but the cross-sectional shape of the convex portion is not limited to this example. The shape may be different between the right and left side surfaces of the convex portion.

In the structure illustrated in fig. 48D, the convex portion 122g can be said to have a structure in which two convex portions having a rectangular cross-sectional shape are stacked. Such a sectional shape includes a portion whose height sharply changes when viewed along the arrangement direction. However, if the displacement w of the two rectangles in the arrangement direction is large, the same effect as when the inclination angle of the side surface is made small can be obtained. In other words, the ratio of high-order light in the light of a specific wavelength emitted from the light-emitting element in a specific direction can be reduced. The number of steps in the stepped side surface can also be set arbitrarily. If the number of steps in the stepped side surface is increased, the sectional shape of the convex portion is close to a triangle, and thus the proportion of high-order light can be similarly reduced.

[ 11-7 ] method for controlling the cross-sectional shape of the surface Structure ]

As described above, the periodic structure 120a can be formed on the substrate 140 by applying a method such as a semiconductor process or nano imprint. Then, by forming a film of a fluorescent material on the substrate 140 by, for example, sputtering, it is possible to form the photoluminescent layer 110 and the periodic structure 120b including a plurality of convex portions (or concave portions) corresponding to the plurality of convex portions (or concave portions) constituting the periodic structure 120 a.

When the periodic structure 120b is formed, the cross-sectional shape of the plurality of projections (or recesses) constituting the periodic structure 120b can be controlled by adjusting the pressure of the ambient gas (e.g., argon gas) during sputtering. If the pressure during sputtering is low, ballistic transport is dominant, and as schematically shown in fig. 49A, material particles emitted from the target collide approximately perpendicularly with the surface of the substrate 140. Therefore, the cross-sectional shapes of the plurality of projections constituting the periodic structure 120a on the substrate 140 are easily reflected in the cross-sectional shapes of the plurality of projections of the periodic structure 120 b. Further, collision of molecules constituting the atmosphere easily acts similarly to dry etching, and the corner tends to be sharper. On the other hand, if the pressure during sputtering is high, diffusive transport is dominant, and as schematically shown in fig. 49B, the proportion of material particles colliding with the substrate 140 from a direction inclined with respect to the surface of the substrate 140 increases. As a result, a smoother surface is easily formed.

FIGS. 50A and 50B show the results obtained by depositing YAG: ce, vertical cross section of the sample. Fig. 50A and 50B show cross sections of samples on which film formation was performed under ambient gas pressures of 0.3Pa and 0.5Pa, respectively. In both of the samples shown in fig. 50A and 50B, film formation was performed in a state in which a quartz substrate was disposed directly below the ablation region of the target (the region where material particles were ejected from the target).

Further, by adjusting the heights of the plurality of convex portions (or the depths of the concave portions) constituting the periodic structure 120a on the substrate 140, the relationship between the width of the top portion of the convex portion (or the width of the opening portion of the concave portion) of the periodic structure 120a and the width of the base portion of the convex portion (or the width of the bottom portion of the concave portion) of the periodic structure 120b on the photoluminescent layer 110 can be controlled.

Fig. 51A and 51B schematically show the cross-sectional shape of the film of the photoluminescent material obtained when the height of the convex portion in the periodic structure 120a on the substrate 140 is relatively small. Fig. 51B shows a state in which the photoluminescent material is further deposited from the state shown in fig. 51A. In fig. 51, attention is paid to a certain convex portion in the periodic structure 120a and a convex portion in the periodic structure 120b corresponding to the convex portion. When the height of the convex portion in the periodic structure 120a is relatively small, the width Bs of the base portion of the convex portion of the periodic structure 120b tends to be smaller than the width Tp of the top portion of the convex portion of the periodic structure 120 a. If it is considered that a concave portion is formed between two adjacent convex portions in the periodic structure 120a and a concave portion corresponding to the concave portion is formed between two adjacent convex portions in the periodic structure 120b, the width Bm of the bottom portion of the concave portion of the periodic structure 120b is larger than the width Op of the opening portion of the concave portion of the periodic structure 120 a.

FIG. 51C shows a case where YAG is deposited by sputtering on a quartz substrate having a periodic structure (period: 400nm) including a plurality of projections having a rectangular cross-sectional shape and a height of 60 nm: ce, vertical cross section of the sample. In the sputtering, the pressure of the ambient gas was set to 0.5Pa, and the quartz substrate was disposed directly below the ablation region of the target.

Fig. 52A and 52B schematically show the cross-sectional shape of the film of the photoluminescent material obtained when the height of the convex portion in the periodic structure 120a on the substrate 140 is relatively large. Fig. 52B shows a state in which the photoluminescent material is further deposited from the state shown in fig. 52A. In fig. 52B, attention is paid to a certain convex portion in the periodic structure 120a and a convex portion in the periodic structure 120B corresponding to the convex portion. When the height of the convex portion in the periodic structure 120a is relatively large, the width Bs of the base portion of the convex portion of the periodic structure 120b tends to be larger than the width Tp of the top portion of the convex portion of the periodic structure 120 a. If it is considered that a concave portion is formed between two adjacent convex portions in the periodic structure 120a and a concave portion corresponding to the concave portion is formed between two adjacent convex portions in the periodic structure 120b, the width Bm of the bottom portion of the concave portion of the periodic structure 120b is smaller than the width Op of the opening portion of the concave portion of the periodic structure 120 a.

FIG. 52C shows a case where YAG is deposited by sputtering on a quartz substrate having a periodic structure (period: 400nm) including a plurality of projections having a rectangular cross-sectional shape and a height of 200 nm: ce, vertical cross section of the sample. The pressure of the ambient gas during sputtering was 0.5 Pa. In this example, the quartz substrate was deposited in a state where it was disposed at a position slightly shifted from the position immediately below the ablation region of the target. Therefore, it is found that the center of gravity of the lower convex portion (convex portion formed on the quartz substrate) and the center of gravity of the upper convex portion (convex portion formed on the YAG layer) are slightly shifted in the arrangement direction.

[ 11-8. offset of periodic structure 120b relative to periodic structure 120a ]

In the structures illustrated in fig. 43 and 45, the plurality of projections of the periodic structure 120b are located directly above the plurality of projections of the periodic structure 120a, respectively. However, as illustrated in fig. 52C, the centers of the convex portions (or concave portions) on the substrate 140 and the corresponding convex portions (or concave portions) on the photoluminescent layer 110 do not necessarily coincide completely. As described below, in the periodic structure 120a on the substrate 140 and the periodic structure 120b on the photoluminescent layer 110, a higher effect of enhancing light emission may be obtained with one of them as a reference and the other shifted by a certain amount in the arrangement direction.

The inventors of the present invention verified, by optical analysis, that the amount of shift of the periodic structure 120b on the photoluminescent layer 110 in the alignment direction with respect to the periodic structure 120a on the substrate 140 affects the degree of enhancement of light. For optical analysis, Diffract MOD (サイバネット Co.) was used. As a model for calculation, a structure having a 1-dimensional periodic structure uniform in the y direction is formed on the substrate 140 and the photoluminescent layer 110, as in the example described with reference to fig. 44 and the like. However, here, as shown in fig. 53, the calculation was performed assuming that the cross-sectional shape of each convex portion in the periodic structure 120a and the periodic structure 120b is rectangular (the inclination angle of the side surface is 90 °).

Fig. 53 is a schematic cross-sectional view for explaining an offset amount between the periodic structure 120a and the periodic structure 120 b. The amount of displacement between the periodic structures can be represented by the magnitude of the shift along the arrangement direction with respect to the period of the periodic structures. The magnitude of the shift along the arrangement direction is defined as, for example, a distance St along the arrangement direction between a position of the right end of the base of the convex portion in the periodic structure 120a and a position of the right end of the base of the corresponding convex portion in the periodic structure 120b, as shown in the drawing. In fig. 53, the uppermost cross section is a state where the offset St is 0, and the lowermost cross section is a state where the offset St is 50% of the cycle. In the present specification, a state in which a certain convex portion (or concave portion) in the periodic structure 120a and a certain convex portion (or concave portion) in the periodic structure 120b are shifted in the arrangement direction in a range of not more than 50% of the period is expressed as "corresponding".

Fig. 54 shows the result of calculating the degree of enhancement of light emitted in the front direction by changing the amount of shift of the periodic structure 120b with respect to the periodic structure 120 a. As shown in fig. 54, as the shift amount increases, the peak value of light emission becomes higher. However, if the amount of deviation reaches 50% of the period of the periodic structure, the peak value decreases compared to the case where the amount of deviation is 40%. Here, in the case where the shift amount is 30% and 40% of the period, a high effect of light emission enhancement is obtained.

As is clear from fig. 54, by shifting the periodic structure 120a on the substrate 140 and the periodic structure 120b on the photoluminescent layer 110 in the alignment direction with an upper limit of 50% of the period, a higher effect of enhancing light emission may be obtained for a specific wavelength. In this way, between the plurality of projections (or recesses) in the periodic structure 120a on the substrate 140 and the plurality of projections (or recesses) in the periodic structure 120b on the photoluminescent layer 110, it is not necessary that their centers completely coincide, and a certain degree of deviation is allowed.

Industrial applicability

The light-emitting element and the light-emitting device of the present invention are represented by a lighting fixture, a display, and a projector, and can be applied to various optical devices.

Description of the reference symbols

100. 100 a-100 c light emitting element

110 photoluminescent layer (guided wave layer)

120. 120', 120 a-120 g light-transmitting layer (periodic structure, submicron structure)

140 base plate

150 protective layer

180 light source

200 light emitting device

Claims

1. A light-emitting element, characterized in that:

have:

a light-transmitting layer having a first surface;

The photoluminescent layer is located on the first surface, has a second surface on the light-transmitting layer side and a third surface on the opposite side of the second surface, receives excitation light and emits wavelengths including air from the third surface is the light of the first light of λ _a ;

The photoluminescent layer has a first surface structure including a plurality of convex portions on the third surface;

The light-transmitting layer has a second surface structure including a plurality of protrusions corresponding to the plurality of protrusions on the first surface;

The first surface structure and the second surface structure restrict the directivity angle of the first light emitted from the third surface;

The plurality of protrusions in the first surface structure include a first protrusion;

In the cross section perpendicular to the photoluminescent layer and parallel to the arrangement direction of the plurality of convex portions in the first surface structure, the width of the base portion of the first convex portion is larger than the width of the top portion,

The first surface structure and the second surface structure are formed inside the photoluminescent layer so that the intensity of the first light emitted from the third surface is predetermined by the first surface structure and the second surface structure. is the largest simulated guided wave mode in the 1st direction.

2. The light-emitting element according to claim 1, wherein

The inclination angle of the side surface of the said some convex part in the said 1st surface structure is smaller than the inclination angle of the side surface of the said some convex part in the said 2nd surface structure.

3. The light-emitting element according to claim 1, wherein

The second surface structure includes a second convex portion corresponding to the first convex portion;

In the cross section, the width of the base portion of the first convex portion is smaller than the width of the top portion of the second convex portion.

4. The light-emitting element of claim 1, wherein

In the cross section, the width of the base portion of the first convex portion is larger than the width of the top portion of the second convex portion.

5. The light-emitting element according to claim 1, wherein

The plurality of protrusions in the second surface structure include second protrusions corresponding to the first protrusions;

In the cross section, the width of the base portion of the second convex portion is larger than the width of the top portion of the second convex portion.

6. The light-emitting element according to claim 5, wherein

At least a part of side surfaces of the plurality of convex portions in the first surface structure is inclined with respect to a direction perpendicular to the photoluminescent layer;

At least a part of the side surface of the said some convex part in the said 2nd surface structure is inclined with respect to the direction perpendicular|vertical to the said photoluminescent layer.

7. The light-emitting element according to claim 5, wherein

At least one of at least a portion of the side surfaces of the plurality of convex portions in the first surface structure and at least a portion of the side surfaces of the plurality of convex portions in the second surface structure is stepped.

8. The light-emitting element according to any one of claims 1 to 7, wherein

Assuming that the distance between two adjacent convex portions in the first surface structure is D1 _int , the distance between two adjacent convex portions in the second surface structure is D2 _int , and the photoluminescent layer is When the refractive index of the first light is n _wav-a , the relationships of λ _a /n _wav-a <D1 _int <λ _a and λ _a /n _wav-a <D2 _int <λ _a hold.

9. The light-emitting element of claim 8, wherein

The above D1 _int is equal to the above D2 _int .

10. A light-emitting element, characterized in that:

have:

a light-transmitting layer having a first surface;

The photoluminescent layer has a first surface structure including a plurality of recesses on the third surface;

The light-transmitting layer has a second surface structure including a plurality of recesses corresponding to the plurality of recesses on the first surface;

The plurality of recesses in the first surface structure include a first recess;

In the cross section perpendicular to the photoluminescent layer and parallel to the arrangement direction of the plurality of recesses in the first surface structure, the width of the opening of the first recess is larger than the width of the bottom,

The first surface structure and the second surface structure are formed inside the photoluminescent layer so that the intensity of the first light emitted from the third surface is predetermined by the first surface structure and the second surface structure. is the largest simulated guided mode in the 1st direction.

11. The light-emitting element according to claim 10, wherein

The inclination angle of the side surface of the said some recessed part in the said 1st surface structure is smaller than the inclination angle of the side surface of the said several recessed part in the said 2nd surface structure.

12. The light-emitting element of claim 10, wherein

The second surface structure includes a second recess corresponding to the first recess;

In the cross section, the width of the bottom portion of the first recessed portion is smaller than the width of the opening portion of the second recessed portion.

13. The light-emitting element of claim 10, wherein

In the cross section, the width of the bottom portion of the first recessed portion is larger than the width of the opening portion of the second recessed portion.

14. The light-emitting element of claim 10, wherein

The plurality of recesses in the second surface structure include second recesses corresponding to the first recesses;

In the cross section, the width of the opening of the second recess is larger than the width of the bottom of the second recess.

15. The light-emitting element of claim 14, wherein

At least a part of side surfaces of the plurality of recesses in the first surface structure is inclined with respect to a direction perpendicular to the photoluminescent layer;

At least a part of the side surface of the said some recessed part in the said 2nd surface structure is inclined with respect to the direction perpendicular|vertical to the said photoluminescent layer.

16. The light-emitting element of claim 14, wherein

At least one of at least a part of the side surfaces of the plurality of recesses in the first surface structure and at least a part of the side surfaces of the plurality of recesses in the second surface structure is stepped.

17. The light-emitting element according to any one of claims 10 to 16, wherein

Assuming that the distance between two adjacent recesses in the first surface structure is D1 _int , and the distance between two adjacent recesses in the second surface structure is D2 _int , it is assumed that the photoluminescence layer has a 1 If the refractive index of light is n _wav−a , the relationships of λ _a /n _wav−a <D1 _int <λ _a and λ _a /n _wav−a <D2 _int <λ _a hold.

18. The light-emitting element according to any one of claims 1 to 7 and 10 to 16, wherein

The above-mentioned first surface structure has at least one first periodic structure;

The above-mentioned second surface structure has at least one second periodic structure;

If the period of the at least one first periodic structure is p1 _a , the period of the at least one second periodic structure is p2 _a , and the refractive index of the photoluminescent layer with respect to the first light is n _wav-a , then the relationship of λ _a /n _wav-a <p1 _a <λ _a and λ _a /n _wav-a <p2 _a <λ _a holds.

19. The light-emitting element according to claim 1 or 10, wherein

The first light emitted in the first direction is linearly polarized light.

20. The light-emitting element according to any one of claims 1 to 7 and 10 to 16, wherein

The said 1st surface structure and the said 2nd surface structure restrict the directivity angle of the said 1st light emitted from the said 3rd surface to be less than 15 degrees.